Reuters photographer Namir Noor-Eldeen and the driver Saeed Chmagh were among those killed.
The agency has long pressed for the release of the black-and-white aerial video, and conversations between the pilots in two Apache helicopters as they open fire on people on a street in Baghdad.
WikiLeaks said it had acquired the video from whistleblowers in the military and viewed it after breaking the encryption code.
In the recording, the helicopter crew can be heard discussing the scene on the street below, where one American claims to have spotted six people with AK-47s and one with a rocket-propelled grenade.
One of the helicopter crew is then heard saying that one of the group is shooting, but the video shows there is no shooting or even a pointing of weapons.
The pilots believe them to be insurgents, and mistake Noor-Eldeen's camera for a weapon.
"Look at those dead bastards," The New York Times quoted one pilot, as saying.
"Nice," the other responds.
A wounded man can be seen crawling on the street. Couple of minutes later, the pilots open fire at a van, which had came to pick up the injured, wounding two children inside.
"Well, it's their fault for bringing their kids into a battle," one pilot said.
David Schlesinger, the editor in chief of Reuters, said in a statement that the video was "graphic evidence of the dangers involved in wartime journalism and the tragedies that can result."
The footage will further anger the Pentagon, which has drawn up a report identifying the whistleblower website as a threat to national security.
This tragic incident was investigated at that time by the brigade involved and the investigation found that the forces involved were not aware of the presence of the two reporters, and that all evidence available supported the conclusion by those forces that they were engaging armed insurgents, and not civilians," Maj. Shawn Turner, a U.S. military spokesman, told CNN in a written statement Monday.
The Army's 2007 report on the incident found the crew had "neither reason nor probability to assume that neutral media personnel were embedded with enemy forces," according to a copy of the document released to CNN.
"We regret the loss of innocent life, but this incident was promptly investigated, and there was never any attempt to cover up any aspects of this engagement," Turner added.
As many as 139 journalists, nearly 120 of them Iraqis, have been killed during the 7-year-old war, according to the Committee To Protect Journalists. Reuters said the deaths of Chmagh and Noor-Eldeen "were tragic and emblematic of the extreme dangers that exist in covering war zones."
article