A key witness in the investigation by special counsel Robert S. Mueller III traveled from abroad to the United States four times to speak to agents, despite having provided them with a phone that the government says contained child pornography, his attorneys said Friday.

Attorneys for George Nader revealed that information in Alexandria federal court Friday as part of an unsuccessful effort to argue that the Lebanese American businessman could be safely released from jail while facing trial for transporting sexually explicit videos of young boys.

Prosecutors countered that Nader was both a flight risk and a danger to the community. Assistant U.S. Attorney Jay Prabhu sketched Nader’s history of crimes involving minors, including a 1991 conviction for child porn transportation in Alexandria.

When he was stopped at Dulles International Airport in January 2018, Nader had on his phone a dozen sexual videos of boys as young as 2 years old that had been shared with “multiple people,” Prabhu said.

Prabhu said that in both 1997 and 2002, Nader brought 14-year-old boys into the United States; one told FBI agents he watched child pornography with the older man and the other said he was sexually abused. In 2003, Nader was convicted in the Czech Republic of what his attorney Christopher Clark described in court as “contributing to the moral corruption of society.”

Nader has had “hands-on contact with more than a dozen minor boys,” Prabhu said.

Clark said one of the teen boys who spoke to U.S. law enforcement “besmirched Mr. Nader’s name.” But he acknowledged that in the Czech Republic case, Nader admitted to “having a relationship with two young men two years under the age of consent.” The age of consent in the Czech Republic is 15.

Nader has never been charged with a crime in the United States involving physical contact with children. He was indicted in 1984 for child pornography possession in the District of Columbia, but successfully argued that it was found through an illegal search. Child porn was found in his possession again in subsequent years, according to prosecutors, but he was not charged again until 1990, when he was caught at Dulles with explicit films featuring minor boys.

Clark emphasized that according to law enforcement, Nader knew there was child pornography on his phone when it was searched by FBI agents in 2018. Yet, he said, “Mr. Nader . . . comes back to the U.S. four times . . . to meet with the FBI” as part of the Russia investigation. “They didn’t move for a year to apprehend him,” Clark added. “He always comes back to the U.S.”

Nader came to the United States from Germany last week for an evaluation after undergoing triple bypass surgery, his lawyers said. They had hoped to see him put under private armed guard at Inova Fairfax Hospital while his criminal case is pending, an accommodation Judge Ivan D. Davis rejected.

“He’s not gotten any better,” Davis said of Nader’s alleged conduct.

Nader served in early 2017 as a kind of liaison between allies of the incoming Trump administration and figures in the Middle East and Russia who hoped to influence U.S. policy. He helped arrange a meeting in the Seychelles in January 2017 between Erik Prince, a Trump supporter who founded the private security firm Blackwater, and a Russian official close to Russian President Vladi­mir Putin. The purpose of the meeting was of particular interest to Mueller’s investigators, and some questions about it remain unanswered, even after Mueller issued a 448-page report on his findings.

Nader was born in Lebanon and came to the United States as a teen. He later founded Middle East Insight, a magazine dedicated to coverage of the region — a role that led him to travel frequently and interview world leaders and top U.S. politicians.

In the 1980s, he developed a reputation as a back-channel negotiator with access to top officials in Israel, Syria and Iran, as well as leaders of the Hezbollah movement, according to people familiar with his work. In the past few years, he has worked as an adviser to senior officials in the United Arab Emirates.

Nader had numbers in his phone for senior leaders in the United States and Saudi Arabia, prosecutors said, and he has homes in Lebanon and the UAE, along with millions of dollars in assets.