WASHINGTON — How did George Nader — Lebanese-American businessman, globe-trotting ‘‘fixer,’’ convicted child molester — get caught up in Special Counsel Robert Mueller’s investigation?

The answer, it seems, can be found in the shadows, where Nader has long operated.

His long history included intrepid back-channel mediation between Israel and Arab countries — and a 15-year-old pedophilia conviction in Europe that has not been previously reported. But Mueller, in his investigation of President Trump, his campaign, and possible wrongdoing connected to Russia, is focused on Nader’s role in two high-level get-togethers after the presidential election, according to three people familiar with the case.

Nader was caught in Mueller’s web a few days before the anniversary of Trump’s inauguration. He was transiting through Dulles International Airport outside Washington, on his way to Trump’s Mar-a-Lago resort, when his plans changed — abruptly and involuntarily.

Mueller’s investigators stopped him, people familiar with the case said. His electronics were seized and he was then allowed to go see his lawyer. Nader later agreed to cooperate with Mueller’s investigation, said the people with knowledge of the case as it pertains to Nader. They weren’t authorized to speak publicly on the case and demanded anonymity.

Nader is little known to the public, a man who has led a shadowy existence as a go-between across numerous Middle East capitals and who gave testimony to Mueller’s Washington grand jury earlier this month.

Nader joined a meeting at New York’s Trump Tower in December 2016 that brought together presidential son-in-law Jared Kushner, chief strategist Steve Bannon — fired by Trump last August — and Mohammed bin Zayed, crown prince of Abu Dhabi and de facto leader of the United Arab Emirates.

A second meeting occurred a month later in the Indian Ocean archipelago of Seychelles and involved Nader, bin Zayed, former Blackwater boss Erik Prince, and Kirill Dmitriev, a Russian banker close to President Vladimir Putin.

Nader’s record of sexual abuse in Prague appears unrelated to his role in Mueller’s probe in the United States; it is unclear whether Mueller’s investigators knew about it. One of Nader’s lawyers, Sandeep Savla, suggested that information about his record was being leaked to stop him from cooperating.

Two people with knowledge of the case confirmed it involved the same Nader now cooperating with Mueller.