Rep. Devin Nunes, R-Calif., is requesting documents from a slew of federal agencies about Maltese academic Joseph Mifsud, the man who told former Trump campaign adviser George Papadopoulos the Russians had thousands of Hillary Clinton's emails.

The House Intelligence Committee ranking member seeks information about who Mifsud was working for at the time and wrote in a letter that special counsel Robert Mueller “omits any mention of a wide range of contacts Mifsud had with Western political institutions and individuals" in his report on Russian interference in the 2016 election.

Mifsud, a London-based professor, has long been suspected to have deep ties to Russian intelligence and is an elusive figure that has stayed out of the spotlight in recent years.

Mueller's 448-page report, released last month with redactions, states that Mifsud traveled to Moscow in April 2016, after which he met Papadopoulos in London. It was at this meeting that Mifsud informed Papadopoulos that during his trip he learned that the Russians had “dirt” on Clinton, President Trump's Democratic rival in the 2016 election. Papadopoulos later repeated this claim to Australian diplomat Alexander Downer, who informed the FBI and prompted the original counterintelligence investigation into President Trump's campaign in July 2016.

As part of Mueller’s Russia investigation, Papadopoulos pleaded guilty in October 2017 to making false statements to the FBI about his contacts with Russians and served 12 days in prison late last year.

The FBI interviewed Mifsud in the U.S. about his communications with Papadopoulos in early February 2017. The special counsel’s sentencing memo to the District Court for the District of Columbia said Papadopoulos hindered the FBI's ability to "challenge" Mifsud. "The defendant’s lies undermined investigators’ ability to challenge the Professor or potentially detain or arrest him while he was still in the United States. The government understands that the Professor left the United States on February 11, 2017 and he has not returned to the United States since then," the memo said.

In his letter, Nunes says it is "still a mystery how the FBI knew to ask Papadopoulos specifically about Hillary Clinton’s emails" if the bureau had not spoken with Mifsud.

Nunes asks Central Intelligence Agency Director Gina Haspel, FBI Director Chris Wray, National Security Agency Director Paul Nakasone, and Secretary of State Mike Pompeo to hand over all documents they have on Mifsud by May 10.

The letter, obtained by the Washington Examiner, contains photographic evidence of Mifsud in close proximity to Western officials.

"If he is in fact a Russian agent, it would be one of the biggest intelligence scandals for not only the United States, but also our allies like the Italians and the Brits and others. Because if Mifsud is a Russian agent, he would know all kinds of our intelligence agents throughout the globe," Nunes said during an interview with Fox News' Sean Hannity.