Lawyers for Nader did not return calls seeking comment.
If convicted, Nader could face a minimum of 15 years in prison and a maximum of 40 years, officials said.
Nader was known to Trump associates as someone with political connections in the Middle East who could help them navigate the diplomacy of the region.
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.
A Lebanese American businessman, Nader was stopped by federal agents when he arrived at Dulles in January 2018. Those FBI agents served him with a subpoena and wanted to question him as part of the Russia investigation, according to people who, like others familiar with the issue, spoke on the condition of anonymity to discuss sensitive matters.
According to the complaint, Nader was interviewed by FBI agents at the airport, and one of his three iPhones was searched for reasons unrelated to child pornography. But on the phone, authorities found 12 sexually explicit videos featuring boys ranging in age from 2 to 14, according to the court documents.
Over the following weeks, Nader began to cooperate with authorities, providing grand jury testimony about his interactions with Trump supporters, according to people familiar with the matter.
Authorities said he was charged under seal on the alleged child pornography in April 2018, but he had left the country at that point.
Prince has insisted, publicly and to Congress, that his meeting in the Seychelles with Kirill Dmitriev, the head of a Russian government-controlled wealth fund, was a chance encounter that occurred because he happened to be meeting with United Arab Emirates officials at a luxury hotel in the Indian Ocean nation.
At the time, Nader had been working for years as an adviser to the UAE. Nader told investigators it was a meeting planned in advance, as an exploratory back channel between a Trump emissary and a Kremlin official, to allow for informal discussions of future relations between the two countries, according to people familiar with the investigation.
Nader also visited the White House several times after the Seychelles encounter, according to people familiar with his visits, meeting with senior advisers Steve Bannon and Jared Kushner, the latter of which is the president's son-in-law.
Nader was convicted 28 years ago of transporting child pornography, a case in which he received a reduced sentence after influential figures argued privately to the court that he was playing a valuable role in national security affairs - trying to free US hostages then held in Lebanon.
Born in Lebanon, Nader came to the US as a teen and 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 US 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 Hizbollah movement, according to people familiar with his work. In the past few years, he has worked as an adviser to senior officials in the UAE.
Amid his international work, Nader had repeatedly been investigated by law enforcement officials, according to court filings.
In 1985, he was indicted by a federal grand jury in Washington on two counts of mailing and importing child pornography. Court documents show that those charges were dismissed before trial after Nader's lawyers successfully argued that authorities had illegally seized evidence in the case. Records show that Nader became a US citizen while awaiting trial in the case.
During two instances in 1988, Nader received sexually explicit material, featuring underage boys, sent to him via a post office box in Cleveland, according to court filings. He was not charged, although his home was searched, and prosecutors say child pornography was found in his toilet.
In the 1991 case, Nader pleaded guilty to one count of transporting child pornography and served about six months in federal custody in a facility on work release, court records show.
Nader had powerful supporters who appealed to the court on his behalf, arguing that he was engaged in high-stakes negotiations to assist the US government in freeing hostages in Lebanon.
Nader was ultimately given consideration in his sentence because of what a federal judge termed his "extraordinary cooperation with the government in certain areas," according to court documents.
More recently, AP has reported that Nader was convicted of 10 cases of sexually abusing minors in Prague in May 2003 and was sentenced to one year in prison. His expulsion from the country was also ordered. Nader's lawyers have previously declined to comment on the Prague case.
