We read hundreds of pages of emails that Congress collected from the biggest tech companies in the world — here are the most revealing things we found

It shows industry leaders strategizing ahead of decisions that would become turning points in the legacy of their businesses, such as Facebook's $1 billion acquisition of Instagram and Amazon's decision to undercut prices for diapers to compete with Diapers.com.

The four companies turned over the documents at the request of the committee. But the huge trove of evidence is likely just a fraction of that which federal and state regulators have been poring over as they decide whether to bring an antitrust case against any of the tech giants. Google appears to be most immediately in danger of such an outcome, as The Wall Street Journal reported earlier this year that the Department of Justice is gearing up to announce an antitrust case as soon as this summer.

In some cases, regulators may have had these documents before, such as when requesting more information on a potential deal. Alicia Batts, an antitrust expert who previously worked as an attorney at the Federal Trade Commission and in private practice, said it's not uncommon for "bad documents" to surface in a merger investigation.

"It's an indication to look deeper but not necessarily an indication you won't be able to close [the deal]," she said in an interview this week with CNBC. "When you have both documents that show a company is planning to harm competition and the economic data or the economic model support that it's possible, that's when the documents are given the most weight."

CNBC dug through the hundreds of pages released by the House Judiciary Committee last week to find the most revealing details laid bare in the companies' private correspondence. 

Here are the most notable finds and what they could mean for a potential antitrust case against each company.

What an antitrust case could look like: Experts speculate that an antitrust case against Facebook would center largely around its acquisition strategy and whether it broke merger laws by buying up a nascent competitor or violated anti-monopoly law by taking anti-competitive actions to build or maintain dominance in its market.

Most interesting finds: The most compelling documents released by the committee on Facebook reveal top executives' thinking behind its acquisition of Instagram, one of the two deals that are now thought to have played a key role in Facebook's continued growth, along with its acquisition of WhatsApp. Some enforcement advocates, such as Columbia Law School professor Tim Wu, believe that had those apps not been acquired at an early stage, they could have grown into formidable competitors against Facebook.

- Facebook executives feared decelerating engagement prior to the Instagram deal: Executives fretted about Facebook's relatively weak offerings on mobile, where Instagram had built its growing userbase. 

"We have this big issue right now because gaming is shifting from us to mobile platforms," CEO Mark Zuckerberg wrote in one April 2012 email. "It's causing all this negative momentum in a bunch of ways around gamer overall user engagement, ad spend from gamers, overall revenue, etc." 

- Facebook executives appeared threatened by Instagram's growth in 2012: Zuckerberg acknowledged the threat posed by Instagram in conversations with his deputies. In February 2012, Zuckerberg wrote in an email to then-CFO David Ebersman he was considering how much Facebook should be "willing to pay to acquire mobile app companies like Instagram and Path that are building networks that are competitive with our own." He said that while those competitors have small teams, they have shown fast growth and even if they don't want to sell, a high enough price may change their minds. 

"The businesses are nascent but the networks are established, the brands are already meaningful and if they grow to a large scale they could be disruptive to us," Zuckerberg wrote.

In April 2012, he told one employee in an email, "Instagram can hurt us meaningfully without becoming a huge business though. For the others, if they become big we'll just regret not doing them." 

- Instagram co-founder Kevin Systrom feared Zuckerberg entering "destroy mode" if he didn't sell: As Zuckerberg began to court Instagram for a potential deal, Systrom messaged one of his investors, Benchmark Partner Matt Cohler, in February 2012 for advice on how to politely rebuff an offer. Systrom seemed adamant in wanting to stay independent to see how far he could take Instagram on his own. But he wanted Cohler's advice on whether Zuckerberg would "go into destroy mode" if he rejected an offer. 

"[P]robably," Cohler responded, "(and probably if we just don't engage at all)."

As they strategized the best response, Systrom acknowledged, "bottom line I don't think we'll ever escape the wrath of mark haha[.]"

Later on, messages between Systrom and Zuckerberg leading up to their agreement to merge shed light on what Instagram had to fear if it were to go it alone.

"Of course, at the same time we're developing our own photos strategy," Zuckerberg wrote, "so how we engage now will also determine how much we're partners vs competitors down the line."

What it could mean for a potential antitrust case: Even if regulators believe Facebook executives were afraid of the potential rise of Instagram and WhatsApp, it may not be enough to accuse them of violating merger law. To prove that Facebook violated Section 7 of the Clayton Act through those acquisitions, the FTC may have to prove not only that Instagram and WhatsApp were capable of growing into competitors to Facebook on their own, but also that they were among the very few firms that were committed to getting into Facebook's market and capable of doing so.

"What that means is, if at the time of the acquisition it looks as if Instagram was just one of many nascent folks nibbling at the heels of Facebook, the case law makes it very hard for the government to block that kind of an acquisition," said Bill Baer, a visiting fellow at the Brookings Institution who formerly led the FTC's Bureau of Competition and DOJ Antitrust Division during Democratic administrations.

A Facebook spokesperson confirmed Wednesday that the company had submitted the documents included in the Judiciary Committee file in its disclosure to the FTC in 2012 when the agency reviewed Facebook's proposed acquisition of Instagram. That indicates the FTC determined at the time that those statements did not preclude the merger when weighed against economic models predicting the companies' future success.

But looking back is often easier than looking forward. Showing a pattern of anti-competitive acquisitions or other behavior could potentially help build a case against Facebook under Section 2 of the Sherman Act, the anti-monopoly law, or Section 5 of the FTC Act, which grants what some believe to be broader power to the regulator.

Section 5 empowers the FTC to prevent companies from engaging in "unfair methods of competition in or affecting commerce and unfair or deceptive acts or practices in or affecting commerce."

"When you're talking about Section 5, it's not just [the] Sherman and Clayton Act, but it's kind of the spirit of the antitrust laws," said Batts, the former FTC attorney.

This could also be an issue the House Judiciary Committee tackles with its legislative proposals expected to follow the conclusion of its probe. Lawmakers may determine the bar is too high to decide a deal is anti-competitive and adjust the language to make it easier for authorities to bring a case on such grounds. 

In a statement to CNBC sent several hours after this story's publication Thursday, a Facebook spokesperson defended the company's acquisition of Instagram:

"Instagram has become the app it is today, growing from 30 million users in 2012 to more than a billion today, because of Facebook's significant investment," the statement reads. "We've been clear about the strongly competitive landscape at the time — regulators thoroughly reviewed the deal eight years ago and rightly did not see reason to stop it."

What an antitrust case could look like: An antitrust case for Amazon may resemble the line of thinking Sen. Elizabeth Warren, D-Mass., offered in her presidential campaign platform on breaking up Big Tech. Warren argued large tech companies designated as "Platform Utilities" should not be able to control and participate on their own platforms. The FTC has been talking to third-party sellers on Amazon's platform, according to Bloomberg, following concerns that Amazon undercuts sellers on its marketplace.

A recent Wall Street Journal investigation found that Amazon employees had used internal data to inform their private-label brand strategy and compete with other sellers. Though the employees reportedly used aggregated reports combining multiple sellers' performance, they sometimes contained as few as two sellers, making it easy to extrapolate a single seller's data. Amazon has said it was launching an internal investigation into the allegations by the Journal but said it didn't believe the claims to be true.

Most interesting finds: Amazon's internal emails mostly shed light on the company's acquisition mindset and pricing strategy to compete with Diapers.com before it acquired its parent company.

- Amazon undercut Diapers.com's prices before buying it: A top executive, then-vice president of consumables Doug Herrington, identified Diapers.com as Amazon's "#1 short term competitor" in a 2009 email. "As I've mentioned to each of you, I think, we need to match pricing on these guys no matter what the cost," Herrington wrote.

Over the next year, Amazon began operating its diaper business at a loss, a profit and loss statement shows, offset by other segments of the baby business. 

Once executives learned Diapers.com's parent company, Quidsi, was planning to launch a new vertical, Soap.com, executives crafted a plan to keep it at bay.

"We have already initiated a more aggressive 'plan to win' against diapers.com in the diaper/baby space, which includes market leading pricing on diapers ('double your SNS discount to 30% off diapers and wipes'), a free PRIME offering for new Moms, and a structured and marketed 'Amazon Mom' program," Herrington said. "To the extent this plan undercuts the core diapers business for diapers.com, it will slow the adoption of soap.com."

Amazon announced in 2010 its move to buy Quidsi in a reported $545 million deal, only to shut down the business in 2017 after Amazon said it failed to become profitable.

- Bezos planned to buy "market position - not technology" with Amazon's Ring acquisition: CEO Jeff Bezos acknowledged in an email to executives in 2017 that he wanted to buy doorbell security camera system Ring to solidify market position. 

"To be clear, my view here is that we're buying market position - not technology," Bezos wrote. "And that market position and momentum is very valuable." 

What it could mean for a potential antitrust case: Regulators could use the Diapers.com documents to argue that Amazon engaged in predatory pricing to eliminate a competitor. But doing so is not as easy as showing it discounted goods below its costs, which is a standard competitive practice in some cases and could be considered beneficial for consumers if it results in sustained lower prices.

The FTC says on its website that while prices can at times be "too low," this doesn't happen often.

"Consumers are harmed only if below-cost pricing allows a dominant competitor to knock its rivals out of the market and then raise prices to above-market levels for a substantial time," the agency says. "A firm's independent decision to reduce prices to a level below its own costs does not necessarily injure competition, and, in fact, may simply reflect particularly vigorous competition."

Baer, the former federal antitrust enforcer, said laws prohibiting predatory pricing are not meant to discourage price competition. But discounting could lead to anti-competitive practices when a firm later has the ability to raise prices after eliminating its rival.  

"If you are pricing below an appropriate measure of your cost for the purpose of injuring a competitor and you have the ability to recoup those losses once your competitor is out of business or retreats from its discounting practices, that is potentially an antitrust violation," Baer said.

Still, the documents released by the committee so far don't shed much light on what could become the true focus of an antitrust investigation: how Amazon competes with sellers on its platform. That doesn't mean those documents don't exist, though, or that regulators aren't learning more about those relationships in their interviews with competitors and insiders.

Amazon did not respond to a request for comment.

What an antitrust case could look like: The antitrust theory against Apple centers on its control of the App Store. While iPhones are prevalent throughout the U.S., Apple ranks only third in worldwide market share for smartphones at 13.3%, according to IDC, while the market leader, Samsung, holds a 21.2% share.

A potential case against Apple could look similar to one against Amazon, focusing on the fact that it both owns a marketplace (the App Store) and has its own pre-loaded apps such as Apple Music and Apple Podcasts that compete with other apps on its platform, such as Spotify.

Some developers who offer their apps through the App Store — the only way Apple allows for apps to be added to users' devices — have complained about Apple's opaque and sometimes seemingly arbitrary process for accepting new apps.

Most recently, the founders of Basecamp complained that Apple unfairly rejected their new email app, Hey. Apple had originally claimed it did not meet standards in an early version because it did not offer a way for users to make an account through the app, which would require the developers to give Apple a 30% cut of iOS sign-ups in the first year. An updated version of the app was later approved.

Spotify has been among the most vocal opponents of what it's dubbed the "Apple Tax," the 15% to 30% cut Apple takes for payments processed through apps offered on the App Store. Apple claims the commission covers the cost of running the App Store, but developers have complained that the cost can be prohibitively high and Apple does not provide alternative payment methods. The European Commission recently announced two antitrust probes into Apple's App Store and Apple Pay.

Most interesting finds: The documents released paint a picture that Apple's rules around its App Store may not be as rigid as the company has repeatedly insisted they are.

- Apple executives discussed exceptions to how it applied its App Store rules: Faced with criticism over its opaque enforcement of App Store rules, Apple has publicly stated that it approaches enforcement consistently. 

"We apply the rules to all developers evenly," CEO Tim Cook testified at the antitrust subcommittee hearing last week. 

But internal emails released by the Judiciary Committee show that Apple has at times loosened its rules for some developers. In 2016, for example, Apple senior vice president Eddy Cue told Amazon CEO Jeff Bezos in an email that Apple had agreed to taking only a 15% cut of revenue for customers who sign up for Amazon Prime Video in their iOS app and no cut for already-subscribed customers. 

Although it's unclear from the emails what terms the companies ended up acting on, Cue's promise is different from what Apple typically says it charges developers: a 30% cut of in-app purchase revenue in the first year and 15% every year after for recurring subscriptions.

- Apple's evolving stance on parental control apps frustrated developers, including big brands such as T-Mobile: Several emails included in the release revolve around developers and customers complaining about Apple's enforcement of rules for parental control apps. Apple cracked down on several such apps last year, as The New York Times reported, coinciding with the announcement of Apple's own feature to track screen time. Apple said at the time the removal of the apps was based on the discovery that they could gain too much access to information on users' devices and it was unrelated to the screen time feature launch. In an email responding to a concerned user, Apple's App Store boss Phil Schiller said the technology used to control devices "is not intended to enable a developer to have access to and control over consumers' data and devices, but the apps we removed from the store did just that."

Back in 2018, then-T-Mobile COO Mike Sievert emailed Schiller complaining about its FamilyMode app being removed from the App Store after back and forth with Apple about getting it into compliance. Schiller ended up offering to reinstate the app on the platform for two weeks while T-Mobile worked to remedy the alleged violations.

Apple later loosened its restrictions on parental control apps, causing further frustration for some. One developer complained to Apple executives they had spent $30,000 to retool their parental control app with the guidance of Apple employees only to later find the rule was changed, presumably in such a way that it would not have had to make that investment. Responses from Apple executives to the developer were not included in the documents released.

- Even some Apple employees seemed confused by the company's policies: In a couple of emails, Apple executives seemed unclear on the company's rules or at least acknowledged the ambiguity around its policies.

Emails between public relations executives in 2019 showed those tasked with communicating Apple's views on "right to repair" legislation were unclear on the company's stance. The proposals aimed to make it easier for consumers and third parties to find and offer repair services outside of the manufacturer.

"Right now, it's pretty clear things are happening in a vacuum and there is not an overall strategy," then-director of corporate communications Lori Lodes wrote in a 2019 email. "Plus, with one hand we are making these changes and the other is actively fighting Right to Repair legislation moving in 20 states without real coordination for how updated policies could be used to leverage our position."

In another instance, Cameron Rogers, then senior product manager for artificial reality and virtual reality, told Schiller in a 2019 email that it was unclear to him and others within Apple why a particular gaming app was not included on the App Store.

"It still isn't obvious to people inside the company that work directly on the App Store. I think few people understand the subtleties of the rules as well as you do," Rogers wrote.

- Executives sought to draw a distinction between Google and Apple in arguing it should not be a target of Warren's push to break up Big Tech: Top PR officials at Apple sought to separate their brand from Google's as they discussed how best to respond to Warren's platform of breaking up Big Tech.

Apple's former vice president of communications, Steve Dowling, wrote to his team last year that arguments against Warren's platform should seek to show Apple is not a monopolist ("that's shown by market share") and emphasize, "How do we handle competition with our own apps? We don't do things like pushing down results, etc., as Google (one of her real targets) has." The charge seems to refer to allegations that Google prioritizes its own features in search results or stacks ads at the top of the page. Google has denied unfairly disadvantaging websites in its search product.

What it could mean for a potential antitrust case: Regulators could seek to prove that Apple applies its App Store rules disproportionately to disadvantage rivals. However, they'd likely need to make a credible case that Apple's decisions are fueled at least in part by an attempt to preference its own services, rather than the consumer protection issues it claims to champion. Still, if regulators can show Apple inconsistently applied its rules across developers and made better terms for some for its own business reasons, it could face serious scrutiny.

Apple did not provide a comment on the emails.

What an antitrust case could look like: Google's sprawling business has attracted antitrust scrutiny on multiple fronts. Regulators have looked into Google's search business, online advertising platform and Android mobile operating system. Here's what they might be looking for in each:

- Search: Vertical search competitors such as Yelp and TripAdvisor, which offer search engines for specific purposes such as local businesses or travel, have complained for years that Google prioritizes its own services over their own, including by offering its own competing services above theirs in relevant Google search results.

The FTC has investigated Google's search practices in the past and in 2013, its commissioners unanimously voted to close the investigation. An internal report later obtained by the Journal showed that FTC staff had recommended bringing a case against Google on multiple grounds, though they recommended against a lawsuit over allegations Google favored its own vertical search features over competitors' even though staff said its actions resulted in "significant harm" to rivals.

- Advertising: Google's advertising business has attracted scrutiny over a variety of concerns that essentially boil down to the question of whether Google's expansive control over the digital media supply chain allows other companies to compete. While Google has competitors across many functions of the advertising marketplace, it operates in both the buy side and sell side of transactions, leading to some questions about whether it remains objective about where it routes advertising dollars. Competitors also argue that Google's prices are hard to match because it bundles its ad tools. And on YouTube, Google eliminated the ability to buy ads through third-party services, funneling all spend through its own tools.

- Android: With its Android mobile operating system, Google requires device manufacturers who use its platform to pre-install its app store and other native apps such as Gmail and its Chrome web browser. The European Commission required Google to stop bundling its apps on Android phones and allow EU users to select their default search engine after fining the company $5 billion over alleged antitrust abuse.

Most interesting finds: The internal emails released show how Google executives considered the ways they could position various aspects of the business to become most integral to their users' lives.

- Executives recognized threats from social media platforms and vertical search competitors and aimed to draw users to their own offerings: The documents show Google's fixation on being the leader in search. In a report about how the company would stay ahead in search in 2007, Google said it should "Turn having the largest user base into an unfair advantage by building out tech that improves linearly with user base size." 

The report recognized MySpace "as the clear leader" in people search and social networking at the time. It noted that sites such as MySpace and YouTube "will ultimately represent a threat to our search business as people will spend more time on those sites and ultimately may do most searches from the search boxes available there. They aren't direct competitors, but they may displace us in end-user time tradeoff."

"In the future, we do not want users [to] 'myspace' people for more information. Google should host all information about a person, including myspace info," the report later states.

In 2012, executives discussed their strategy around vertical search, where competitors including Yelp and Booking.com had taken hold. Jeff Huber, a senior vice president who led location services and commerce at the time, explained in an email why he believed it was important to have a presence in verticals such as travel and shopping.

"[I]f we don't have experiences in these areas that are compelling compared to increasingly concentrated branded alternatives, we risk losing relevance overall (e.g., Amazon is increasingly becoming the place you search for things and Google is the place you search for information)."

Still, then-senior vice president of knowledge Alan Eustace warned, "I don't think we want to fight amazon on their turf by building and branding a single purpose experience by a separate team. The same goes for Yelp and Local." Instead, he advocated for an interface that works across several verticals.

- Executives saw a potential deal with YouTube as a way to prevent Yahoo from buying it: As Google executives pondered whether to buy YouTube, one key consideration appeared to be thwarting Yahoo from snatching up the video service.

Huber wrote in a 2005 email, "I think we should talk to them, if nothing else to make it more expensive for Yahoo. They'll also eventually need a monetization/ads model, so we should use ours instead of anything from Yahoo (if they don't go acquisition soon, and we maintain reasonable relations with them)."

Still, then-group product manager Peter Chane wrote that there would be plenty of other acquisition targets for Yahoo to aim for. 

"[I]f we pick them up it would be defensive vs yahoo but there are 20 more sites like this that yahoo could go and buy," he wrote at the time.

Google ended up buying YouTube in 2006 for $1.65 billion after U.S. antitrust regulators reviewed and cleared the deal.

What it could mean for a potential antitrust case: Like the documents released for the other companies, it is hard to point to any email as a smoking gun. But if regulators were to build an antitrust case against Google, documents like these could be used to show patterns in Google's competitive strategy, such as buying a company to prevent a rival from doing it first or building and prioritizing native tools on its search engine platform to keep users from clicking away to competitors' websites.

Google did not provide a comment on the emails, but a spokesperson downplayed the company's dominance in search, saying Amazon gets more searches for consumer products than Google does, for example.

— CNBC's Jessica Bursztynsky, Michelle Gao and J.R. Reed contributed to this report.

Correction: This story has been updated to reflect the correct attribution of the email an Amazon executive sent calling Diapers.com Amazon's "#1 short term competitor."

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