Nicholas Berg, the American businessman executed by Islamic extremists in Iraq, may have had contact with accused Sept. 11 conspirator Zacarias Moussaoui (search).

FBI agents interviewed Berg a few years ago when they were investigating the Sept. 11 terrorist attacks on New York and Washington, sources said. He was interviewed because, unbeknownst to him, Moussaoui had used his e-mail account when he was in Oklahoma.

Sources close to the situation told Fox News that they believed the link to be "coincidental."

On Tuesday, a video surfaced on an Islamic Web site that showed Berg kneeling in front of five men who had their faces covered. After blasting the U.S. government for the prison abuse scandal at Iraq's Abu Ghraib (search) prison, one man takes a long knife and decapitates Berg.

Intelligence officials said Thursday that terror leader Abu Musab al-Zarqawi (search) was most likely the man who beheaded Berg.

The disclosure later Thursday that Berg may have had contact with Moussaoui deepened the mystery of the businessman's plight.

Berg attended the University of Oklahoma (search) and Moussaoui first settled in Norman, Okla., when he came to the United States. The accused co-conspirator used at least one of the university's computers to communicate online, according to the sources.

Sources said that the FBI concluded that Berg had innocently given his e-mail account to someone and it had landed in the hands of other people, including Moussaoui.

The federal government has vowed to seek Moussaoui's execution if he's convicted of participating in a terrorism conspiracy, along with the Sept. 11 hijackers. Moussaoui's lawyers are seeking to rule out the death penalty.