IRS contractor Charles Littlejohn pleaded guilty in October to one count of taking tax return information without authorization. On two separate occasions, Littlejohn provided tax documents belonging to Trump, Jeff Bezos, and Elon Musk to two news organizations.

Littlejohn initially provided The New York Times with 20 years of Donald Trump’s tax returns in 2019, which the news organization published a story about inSeptember 2020.

Federal investigators looking into how the information got into reporters’ hands came up short partly due to Littlejohn’s technical skills, The Journal reported, citing people familiar with the matter. Per the Journal, investigators were unsure if the returns were revealed through a government leak or from someone outside the government who had access to the documents.

That investigation was put to the side due to insufficient concrete information. Later,investigators began looking into a separate incident involving ProPublica, which published dozens of articles in 2021 on the tax returns of uber-wealthy Americans like Amazon’s Bezos and SpaceX CEO Musk.

The amount of information that ProPublica received, which included tax information from thousands of people, indicated to investigators an internal leak from the IRS had occurred, the Journal reported. From there, investigators began combing through employee and contractor search data to see if there were unusual queries that did not align with their specified job descriptions, the Journal reported, citing those same unnamed people.

The Journal reported that these searches weren’t fruitful, but investigators eventually had an unspecified breakthrough in their hunt and focused on Littlejohn. The contractor confessedto leaking the data provided to ProPublica — and to The Times, as well.

The DOJ and attorneys for Littlejohn did not immediately respond to a request for comment sent by Business Insider outside regular business hours.

Littlejohn is set to be sentenced on Monday for a single count of taking tax return information without authorization, as the statute of limitations had passed related to the 2019 leak of Trump’s returns. Republican lawmakers, incensed about the leaks, are demanding that Littlejohn receive a maximum sentence of five years in prison. Prosecutors are also seeking a maximum sentence. Meanwhile, attorneys for Littlejohn have argued that the maximum would be an “extreme” punishment, the Journal reported.

The bombshell reports provided by the Times and ProPublica based on Littlejohn’s leaks revealed that ultrawealthy Americans received massive tax breaks and skirted rules to receive financial benefits.Trump’s tax returns showed the former president paid just $750 in federal income taxes in 2016 and 2017. Bezos’s returns showed that in 2007 and again in 2011, he paid nothing in federal income taxes. Musk’s tax returns showed he paid $455 million in taxes on $1.52 billion in income between 2014 and 2018.

The financial dealings of the ultrawealthy have long been the subject of intense scrutiny. However, few public figures have been subject to as much public interest as former president Trump, who is currently battling an investigation related to his New York business fraud case.

On Friday, a letter written by former federal judge Barbara Jones, the court-appointed special monitor overseeing the fraud case, appeared to indicate that Trump may have engaged in massive tax evasion by claiming he owed more than $48 million in debt to one of his companies — but the loan never existed.