The man was identified as pilot Lyubomir Kostov, according to Mihail Mihailov, the manager of Heli Air, the Bulgarian company that owned the helicopter. He said he saw the video on the Internet and that Kostov was his main pilot.
A spokesman for U.S. forces in Iraq said a U.S. medevac team arrived at the site within half an hour of receiving the report of Thursday's crash and found no survivors.
Arab broadcaster Al-Jazeera, meanwhile, broadcast video Friday that it said was from a separate group calling itself the Mujahedeen Army in Iraq that showed the helicopter crashing to the ground and claiming it shot it down Thursday.
The brief Mujahedeen Army video, aired on Al-Jazeera, shows a helicopter flying about 100 feet above the ground. The camera suddenly shakes, swinging down to show the ground near the cameraman's feet - apparently as the missile hits the helicopter.
When the camera view rights again toward the sky, the helicopter is in flames, arcing toward the ground with a pall of black smoke trailing behind it.
No missile or impact of a missile on the craft is seen. On the right side of the video is a logo of the Mujahedeen Army, and along the bottom the date "21 April 2005" is written in Arabic.
Thursday's chartered flight was believed to be the first civilian aircraft shot down in Iraq since the U.S.-led invasion two years ago.
U.S. officials said they believed the helicopter was shot down by insurgents but could not confirm the cause of the crash. The Bulgarian Defense Ministry said the helicopter was struck by missile fire.
Toronto-based SkyLink Aviation Inc. chartered the helicopter, according to the company's operations manager Paul Greenaway. He said it was flying to Tikrit from Baghdad's heavily guarded Green Zone, home to Iraq's parliament and many diplomats.
The six Americans were helping the Bureau of Diplomatic Security protect U.S. diplomats in Iraq, a U.S. official said. They were employed by Blackwater Security Consulting, a subsidiary of Moyock, N.C.-based security contractor Blackwater USA, which had four employees slain and mutilated by insurgents in Fallujah a year ago - deaths that touched off a Marine assault on insurgents in the city.
Skylink and Blackwater were invited to participate in the investigation, the military said. The Bulgarian government and Heli Air were also sending investigators.
Romanian journalists Ion, 32, Sorin Dumitru Miscoci, 30, and Ovidiu Ohanesian, 37, and Mohammed Monaf, an Iraqi-American who worked as their translator were kidnapped March 28 near their Baghdad hotel shortly after interviewing interim Iraqi Prime Minister Ayad Allawi. They appeared a day later in a video aired on Al-Jazeera.
The video aired Friday shows a man said to be Monaf sitting alone, hands bound. Gunmen stand on either side of him, pointing an automatic rifle and a pistol at his head.
Monaf appealed to President Bush to intervene to help their release, the anchor said.
There was no independent confirmation of the tape's authenticity.
In the footage, the Al-Jazeera anchor said, the woman says that their captors gave the Romanian government four days since the date of broadcast to withdraw its forces from Iraq or else the hostages will be killed.
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Correspondent Veselin Toshkov contributed to this story from Sofia, Bulgaria.
