Washington ? Terrorist Abu Musab al-Zarqawi was the masked man who beheaded an American civilian in Iraq, U.S. intelligence officials concluded Thursday, leaving other questions unresolved about Nicholas Berg’s final days and his contacts with U.S. and Iraqi authorities.

A U.S. diplomat in Iraq told Berg’s family in early April that the self-employed telecommunications businessman was being detained by the U.S. military, according to e-mails the family provided. A State Department spokeswoman said late Thursday that the diplomat got erroneous information from the U.S.-led administration in Iraq before sending the e-mail.

U.S. officials have said Berg, who was found dead last weekend in Baghdad, was detained by Iraqi police March 24 and that he never was in the custody of American forces.

Through a technical analysis, intelligence officials were able to determine “with high probability” that the speaker on a video showing Berg’s beheading was al-Zarqawi, said a CIA official, speaking on condition of anonymity. The same person is shown decapitating Berg, the official said.

U.S. authorities consider al-Zarqawi an ally of Osama bin Laden and say he is running his own terrorist operation.

Three days after Berg’s body was found on Saturday, an Islamic Web site released a video, titled “Sheikh Abu Musab al-Zarqawi slaughters an American infidel with his own hands.”

It shows five armed men disguised by head scarves and masks line up behind Berg, who is seated on the ground. Standing in the middle, the man identified as al-Zarqawi reads a lengthy statement that criticizes Islamic scholars and the “shameful photos” of the humiliation of men and women at the Abu Ghraib prison. He then decapitates Berg.

It is unclear when and how Berg was captured. Accounts of his detention in Mosul in late March are also conflicting.

U.S. officials insist Berg was arrested by Iraqi police for involvement in “suspicious activities.” The Mosul police chief has denied that. An April 1 e-mail from a U.S. consular official in Iraq, provided by Berg’s family, said he was being detained by the U.S. military.

But State Department spokeswoman Kelly Shannon said the e-mail reflected information provided to the diplomat on that day by Coalition Provisional Authority officials in Mosul. Not until April 7, one day after Berg’s release from jail, was the diplomat told that Iraqi police had held Berg, Shannon said.