This post has been updated.

A criminal complaint filed last year but unsealed Monday reveals that Lebanese-American businessman George Nader, a witness in special counsel Robert Mueller’s investigation, was under investigation for transporting child pornography while serving as a witness in the Mueller probe.

Nader was first charged in April 2018, three months after being detained upon arrival at Washington-Dulles Airport by FBI agents working with the Mueller investigation. There, he gave up cell phones where the government allegedly found “visual depictions of minors engaged in sexually explicit conduct.”

An affidavit attached to the criminal complaint against Nader was unsealed Monday, after Nader was arrested once more at New York’s JFK International Airport. The document states that a federal magistrate signed a search warrant for the Middle East-U.S. fixer one day before his January 17, 2018 arrival at Dulles.

“The search warrant pertained to a matter unrelated to child pornography,” the filing reads.

When Nader arrived at the airport from Dubai last year, he was “voluntarily interviewed by FBI agents” about this unrelated matter, the filing reads. At the end of the interview, Nader’s three iPhones were seized pursuant to the search warrant.

The affidavit suggests that the FBI did not discover that Nader was allegedly carrying child pornography until Feb. 12, when “the case agent for that other matter uncovered multiple files which appeared to contain child pornography.”

Nader ultimately spent months cooperating with the Mueller investigation, and testified before a grand jury in the matter.

Investigators were interested in his role in brokering a January 2017 meeting in the Seychelles between Blackwater founder Erik Prince, the crown prince of the UAE, and Russian Direct Investment Fund chief Kirill Dmitriev.

The Mueller report describes Nader as an intermediary between Dmitriev and the Trump transition team. The report says that Dmitriev, acting on orders from Russian President Vladimir Putin, reached out to Nader “to introduce him to Trump transition officials.”

The Mueller report states that Nader “provided information” over multiple interviews, “all but one of which were conducted under a proffer agreement.” The rest of the text in that section is redacted for reasons of grand jury secrecy.

Nader was previously convicted of the same charge — transporting child pornography — 28 years ago. He received a reduced statement after the court was purportedly told that Nader was aiding U.S. national interests in the Middle East.

Nader is set to make an initial court appearance Monday in the Eastern District of New York. The charges were brought in the Eastern District of Virginia.

Read the court filings below.

