The video is the basis of an espionage charge alleging Pfc. Bradley Manning had unauthorized possession of national defense information.
Manning has admitted to leaking the 39-minute cockpit video showing a 2007 attack that killed 11 men, including a Reuters news photographer and his driver. Manning has said he was troubled by the airmen's behavior and by the U.S. military's refusal to release it.
The Pentagon concluded that the troops reasonably mistook the journalists for enemy combatants. WikiLeaks posted it in April 2010 under the title "Collateral Murder."
The 25-year-old soldier from Crescent, Okla., admitted he leaked the video and hundreds of thousands of classified Iraq and Afghanistan war logs and diplomatic cables while working as an intelligence analyst in Baghdad in 2009 and 2010.
Manning says he leaked the material because he was troubled by what it revealed about U.S. foreign policy.
On Monday morning, the defense called its first witness, Chief Warrant Officer 2 Joshua Ehresman, to establish the wide authorized access Manning and other intelligence analysts had. Ehresman testified that Manning and other intelligence analysts scoured a classified computer network for bits of information needed by field commanders.
"We got them wherever we could," Ehresman said. He said the job meant "pulling everything you can from all intelligence assets."
Manning was "the go-to guy" among the analysts in his unit in Iraq and the most productive worker, Ehresman said.
"He was our best analyst by far when it came to developing product," Ehresman said.
Earlier Monday, as the trial entered its sixth week, Manning's defense team asked the military judge to acquit him of as many as seven charges for lack of incriminating evidence. The government has until Thursday to respond, Col. Denise Lind said.
The defense is seeking acquittal on the most serious charge of aiding the enemy, which carries a possible life sentence; a computer fraud charge and as many as five counts of theft. Details of the motions weren't discussed in court.
Manning faces 21 contested counts. The former intelligence analyst pleaded guilty in February to reduced versions of some charges. He faces up to 20 years for the admitted offenses.
The defense has said it intends to call 25 witnesses to refute the government's charges. The 10 prospective witnesses on Monday include Harvard law professor Yochai Benkler, who has written that leaking something to WikiLeaks is no different than leaking it to The New York Times. Benkler's testimony could refute the government's assertion that Manning knowingly gave intelligence to the enemy because he knew al-Qaida members would see what WikiLeaks posted on its website.
Another prospective defense witness, retired Air Force Col. Morris Davis, would likely give testimony to refute charges stemming from Manning's acknowledged leak of Guantanamo Bay detainee assessment records. Morris was the chief prosecutor at Guantanamo from 2005-07.
Manning said in a Feb. 28 courtroom statement that the assessment briefs were "not very important from either an intelligence or national security standpoint."
Michael Navarre, a former Navy judge advocate now in private practice in Washington, said lead defense attorney David Coombs will likely seek to elaborate on Manning's assertion in his February statement that he selectively leaked material that wouldn't harm national security.
"I think he would pick up on the themes he brought out in the plea," Navarre said.