CBS News National Security Correspondent David Martin reports U.S. officials said the FBI questioned Berg, a 26-year-old American civilian who was beheaded in Iraq, in 2002 after a computer password Berg used in college turned up in the possession of Zacarias Moussaoui, the al Qaeda operative arrested shortly before Sept. 11 for his suspicious activity at a flight school in Minnesota.
Moussaoui is now in federal custody and awaiting trial on conspiracy charges stemming from the Sept. 11 attacks.
"The suggestion that Mr. Berg was in some way involved in terrorist activity, or may have been linked in some way to terrorist activity, is a suggestion that we do not have any ability to support and we do not believe is a valid one," Ashcroft said at a news conference.
The 2002 investigation determined that an e-mail address once used by Berg apparently was obtained by the Moussaoui acquaintances while Berg was briefly an engineering student at the University of Oklahoma in 1999.
Berg was buried Friday morning in a private ceremony in Jenkintown, Pa. and a memorial service for Berg's family and friends was planned for Friday afternoon. Family spokesman Bruce Hauser says the memorial will be open only to family and friends.
Berg, a small businessman who went to Iraq seeking a role in reconstruction, was found dead Saturday. On Tuesday, an Islamic Web site posted video in which masked militants beheaded him. The CIA has identified the speaker in the video — the man who murdered Berg — as Abu Musab al-Zarqawi, a terrorist suspected in numerous attacks in Iraq.
Family spokesman Hauser said Berg's mother, father, sister and brother were likely to speak at the private memorial service Friday at a synagogue.
Berg has been remembered by friends as an outgoing and caring soul whose travels to help others took him from abject poverty in Africa to perilous hot spots in Iraq.
Hauser read the following statement at the request of the Berg family:
"A memorial service will be held later today. It is the family's wishes that the service be for friends and family. The synagogue will not be allowing members of the press on their property. Rumors about a media poll are untrue. We're asking that you respect the family's wishes."
In the wake of Berg's gruesome murder, the past link to Moussaoui seems a stranger-than-fiction coincidence — an American who inadvertently gave away his computer password to one suspected al Qaeda operative is later murdered by another notorious al Qaeda operative, Zarqawi.
The slain man's father, Michael Berg, told reporters that his son met Moussaoui while riding the bus to classes, and had allowed the suspect to use his computer.
But the 2002 FBI interview could explain the bureau's interest in Berg while he was detained by authorities in Iraq shortly before the militants kidnapped and killed him.
Berg was picked up on March 24 and released on April 6. The details of that detention are the subject of a dispute between the Berg family and the U.S. government.
The family contends Berg was detained by the U.S. military, and even filed suit seeking his release on April 5. The U.S. military says Iraqi police detained him. Iraqi police deny that.
To back its claims that Berg was in U.S. custody, the family on Thursday gave The Associated Press copies of e-mails from Beth A. Payne, the U.S. consular officer in Iraq.
"I have confirmed that your son, Nick, is being detained by the U.S. military in Mosul. He is safe. He was picked up approximately one week ago. We will try to obtain additional information regarding his detention and a contact person you can communicate with directly," Payne wrote to Berg's father on April 1.
Payne repeated that Berg was "being detained by the U.S. military" in an e-mail the same day to Berg's mother, Suzanne. The next day, Payne wrote that she was still trying to find a local contact for the family, but added that "given the security situation in Iraq it is not easy."
The government says the e-mail from Payne was false. State Department spokeswoman Kelly Shannon said Payne's information came from the Coalition Provisional Authority. The authority did not tell Payne until April 7 that Berg had been held by Iraqi police and not the U.S. military, she said.
"As Mr. Berg had been released, the consular officer did not convey this information to the family because he was released, thankfully," Shannon said. "And we thought he was on his way."
Coalition spokesman Dan Senor said Wednesday that Iraqi police arrested Berg in Mosul on March 24 because local authorities believed he may have been involved in "suspicious activities."
In Mosul, police chief Maj. Gen. Mohammed Khair al-Barhawi insisted Thursday that his department had never arrested Berg and maintained he had no knowledge of the case.
During his detention, Berg was questioned by FBI agents three times.
Berg is believed to have been kidnapped days after Iraqi police or coalition forces released him. The family has blamed the government for keeping him in custody for too long while anti-American violence escalated in Iraq.
Shortly before Berg's disappearance, he was warned by the FBI that Iraq was too volatile a place for unprotected American civilians and that he could be harmed, a senior FBI official, speaking on condition of anonymity, said Wednesday.
Officials said the U.S. government warned Berg to leave Iraq, and offered him a flight out of the country, a month before his grisly death.
The Bergs said they want to know if the government had received an offer to trade Iraqi prisoners for Nicholas Berg. On the videotape of his death, Berg's killers made a reference to a trade offer, but U.S. officials have said they knew of no such offer.
Michael Berg said he wanted to hear President Bush address the issue.
"I would like to ask him if it is true that al Qaeda offered to trade my son's life for the life of another person," Michael Berg said. "And if that is true, well, I need that information. … and I think the people of the United States of America need to know what the fate of their sons and daughters might be in the hands of the Bush administration."
The video in which Berg is killed was titled: "Sheikh Abu Musab al-Zarqawi slaughters an American infidel with his own hands."
The U.S. military has already posted a $10 million reward for Zarqawi for having orchestrated some of the deadliest terrorist attacks in Iraq.
Al-Zarqawi is thought to be in Iraq, operating his own terrorist network, known simply as the "Zarqawi network."