Recently unsealed search warrants against a key witness in special counsel Robert Mueller’s investigation reveal the FBI found child pornography allegedly in his possession during the Russia probe.

Mueller is set to be questioned by two House committees on his investigation Wednesday, where George Nader's role is likely to be scrutinized, given his criminal history.

Federal authorities seized three iPhones from Nader, a wealthy Lebanese American businessman, on Jan. 17, 2018, when he arrived in Washington, D.C., from Dubai.

It’s unclear what authorities obtained the original search warrant for, as it “pertained to a matter unrelated” to child pornography and Nader’s criminal history with that subject matter.

Days later, Nader was voluntarily interviewed by the FBI. Those interviews were also unrelated to child pornography, according to the warrants, and appear to be in reference to Nader’s interviews in the Russia investigation.

According to the Mueller report, Nader was interviewed by the FBI on Jan. 19, 2018, Jan. 22, 2018, and Jan. 23, 2018. He is mentioned in the Mueller report more than 100 times.

“Nader provided information to the office in multiple interviews, all but one of which were conducted under a proffer agreement,” a footnote of the 448-page report says.

The FBI did not discover until Feb. 12, 2018, that Nader’s devices allegedly contained child pornography. He was not charged until April of last year, but by that time he had already left the country for Dubai. The charges were kept under seal and not disclosed to his attorneys even has Nader continued to cooperate in the Mueller investigation, lawyers said.

Nader, 60, did not return to the U.S. until June 3, 2019, when he was arrested at John F. Kennedy International Airport in New York. At the time of his arrest, authorities found four more cellphones in his possession.

He has pleaded not guilty in the case. A trial date has been set for Sept. 30.

Search warrants allege at least a dozen videos containing child porn were found on Nader’s devices, some involving animals and boys as young as two years old.

Nader acted as a connection between President Trump’s circle and Russian and Middle East officials in 2016 and 2017, including helping to set up a January 2017 meeting in the Seychelles between Trump associate and Blackwater founder Erik Prince and a Russian official with close ties to Russian President Vladimir Putin.

Nader pleaded guilty to a federal pornography charge in 1991 and was sentenced to six months in prison. In that case, he was found with two reels of video tape hidden in candy tins when he arrived at the Washington-Dulles International Airport on July 26, 1990.

Czech authorities arrested Nader in April 2002 amid allegations that he had sex with underage boys in the Czech Republic between 1999 and 2002. He was convicted in May 2003 for molesting children, according to the search warrants.

In relation to that case, U.S. authorities interviewed a person referenced as “J.B.” who said he had been sexually abused by Nader in the Czech Republic. Nader transported him to the U.S. when he was 14 years old in 2000 and engaged in sexual acts with the teenager.

Prosecutors made it clear this week that they believed Nader had not changed his criminal behavior over the decades.

“Twenty years later, Defendant has engaged in similar conduct,” investigators alleged in court filings Monday. “Only this time, he concealed the contraband within his cell phones, not candy tins.”

Prosecutors allege Nader has recently “both sent and received child pornography via the WhatsApp messaging application on his phone” and that he has also “responded favorably to a number of his friends’ transmission of videos containing alleged child pornography.”

New evidence uncovered following the seizure of Nader’s iPhone X last month at JFK could lead to further charges against him in the Eastern District of New York, in addition to the charges already brought against him in the Eastern District of Virginia.

“These charges would likely expose Defendant to yet another 15-year (potentially consecutive) mandatory minimum prison sentence for a subsequent conviction growing out of new conduct,” prosecutors said.

On Tuesday, U.S. District Judge Brinkema denied Nader’s request to be released from detention in Virginia.