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Fresh accounts of the Blackwater shooting last month, given by three rooftop witnesses and by U.S. soldiers who arrived shortly after the gunfire ended, cast new doubt Friday on statements by Blackwater guards that they were responding to armed insurgents when Iraqi investigators say 17 Iraqis were killed at a Baghdad intersection. .

The three witnesses, Kurds on a rooftop overlooking the scene on Sept. 16, said they observed no gunfire that could have provoked the shooting by Blackwater guards, and U.S. soldiers who arrived minutes later found shell casings from guns used normally by American contractors as well as the U.S. military.

The Kurdish witnesses are important because they had the advantage of an unobstructed view and because they said they observed the shooting at Nisour Square from start to finish, free from the terror and confusion that might have clouded accounts of witnesses at street level. Moreover, because they are pro-American, their accounts have a credibility not always extended to Iraqi Arabs, who have been more hostile to the U.S. presence.

Their statements, made in interviews with The New York Times, appeared to challenge a State Department account that a Blackwater vehicle had been disabled in the shooting and had to be towed away. Since those initial accounts, Blackwater and the State Department have consistently refused to comment on the substance of the case.

The Kurdish witnesses said that they observed no one firing at the guards at any time , an observation corroborated by the forensic evidence of the shell casings. Two of the witnesses also said all the Blackwater vehicles involved drove away under their own power.

The Kurds work for a political party whose building looks directly down on the square.

“I call it a massacre,” said Omar Waso, one of the witnesses and a senior official at the party, which is called the Patriotic Union of Kurdistan.

Although Blackwater has said its guards were attacked by automatic gunfire, no casings from the sort of guns typically used by insurgents or by Iraqi security forces were found, according to a U.S. military official briefed on the findings of the unit that arrived at the scene about 20 minutes after the Blackwater convoy left. That analysis of forensic evidence at the scene was first reported Friday by The Washington Post.