The question of who detained Berg and why could be important because his detention may have delayed his departure enough that Berg was swept up in the recent escalation of violence in Iraq.
Berg's body was found near a highway overpass in Baghdad on Saturday, the same day he was beheaded, a U.S. official said. A Web site on Tuesday posted video in which he identified himself and was beheaded by masked men who claimed the killing was revenge for the.
That Web site was shut down Thursday by the Malaysian company that hosted it because it was drawing too much traffic.
President Bush said Wednesday that "there's no justification" for the execution of American Nicholas Berg in Iraq.
"The actions of the terrorists who executed this man remind us the nature of a few people who want to stop the advance of democracy," Mr. Bush told reporters on the South Lawn of the White House as he left for an education speech.
According to his family, Berg, a small telecommunications business owner, spoke to his parents on March 24 and told them he would return home on March 30. But he was detained by Iraqi police at a checkpoint in Mosul on March 24.
The family says Berg was turned over to U.S. officials and detained for 13 days.
On April 5, the Bergs filed suit in federal court in Philadelphia, contending that their son was being held illegally by the U.S. military.
The next day Berg was released, the family said. He told his parents he hadn't been mistreated. His family last heard from him April 9 but it was unclear when and where he was abducted.
But coalition spokesman Dan Senor said Wednesday that Berg was never under U.S. custody despite claims from his family.
Senor told reporters that Berg, 26, from West Chester, Pennsylvania, was detained by Iraqi police in Mosul. The Iraqis informed the Americans and the FBI met with Berg three times to determine what he was doing in Iraq.
Senor said that to his knowledge, "he (Berg) was at no time under the jurisdiction or detention of coalition forces."
An FBI statement states, on March 25, "the U.S. military notified FBI Agents in Iraq that the Iraqi Police had detained a U.S. person in Mosul, Iraq. The U.S. person was identified as Nicholas Evan Berg. Mr. Berg had been detained by Iraqi Police who then notified the U.S. military."
However, calls by The Associated Press to police in Mosul failed to find anyone who could confirm Berg was held there or why.
The police chief in Mosul says his forces never detained the American.
The FBI release further states, "During interviews with Mr. Berg, FBI agents and CPA officials emphasized to him the dangerous environment that exists in Iraq, and encouraged him to accept Coalition Provisional Authority's (CPA) offer to facilitate his safe passage out of Iraq. Mr. Berg refused these offers. The CPA coordinated with the Iraqi police for Mr. Berg's release on April 4. He also refused government offers to advise his family and friends of his status."
Senor said "multiple" U.S. agencies would be involved in the Berg case and that the FBI would probably have overall direction.
Senor said that in Iraq, Berg had no affiliation with the United States government, the coalition or "to my knowledge" any coalition-affiliated contractor.
Earlier, a U.S. official, speaking on condition of anonymity, said Berg was in Iraq "of his own accord" and had been advised to leave Iraq but refused.
A memorial for Berg is planned on Friday.
The video in which Berg was killed bore the title "Abu Musab al-Zarqawi shown slaughtering an American," referring to an associate of Osama bin Laden believed behind a wave of suicide bombings in Iraq.
It was unclear whether al-Zarqawi was shown in the video or simply ordered the execution. Al-Zarqawi also is sought in the assassination of a U.S. diplomat in Jordan in 2002. The United States has offered a $10 million reward for information leading to his capture or killing.
The decapitation recalled the kidnapping and videotaped beheading of Wall Street Journal reporter Daniel Pearl in 2002 in Pakistan.
Last month, Iraqi militants videotaped the killing of Italian hostage Fabrizio Quattrocchi, but the Arab TV network Al-Jazeera refused to air it because it was too graphic.
Friends and family of Berg said he— working in Ghana, in one example — and that his going to Iraq fit with that ideology. They said he supported the Iraqi war and the Bush administration.
"He was so upbeat about the things he was witnessing in Iraq. And he wanted to be part of that rebuilding process using his skills," David Skalish, a longtime friend of the victim, told CBS News' Early Show.
In Malaysia, a senior officer of the Web hosting company, Acme Commerce Sdn. Bhd., said Thursday it was not aware that the site, www.al-ansar.biz, may have been connected to al Qaeda or that offensive material had been posted on it.
If it had, the company would likely have shut it down earlier, said Alfred Lim, Acme Commerce's business manager.
"We are a legitimate business, in no way related to al Qaeda," Lim told The Associated Press. "We have no control over what our clients put on their Web sites."
Lim said Acme Commerce disabled the site Thursday morning because it had attracted "a sudden surge of massive traffic that is taking up too much bandwidth and causing inconvenience to our other clients."