Attorneys for Bradley Manning, the Army private who leaked hundreds of thousands of classified documents to the anti-secrecy group WikiLeaks, opened the defense portion of his court-martial Monday with the screening of a cockpit video showing a controversial U.S. helicopter attack in Baghdad in 2007.

The 39-minute video, called “Collateral Murder” when it was posted by WikiLeaks in 2010, captured the killing of a Reuters cameraman and his driver, among 12 casualties, and the Pentagon concluded that the pilots mistook them for enemy fighters during street battles in the Iraqi capital.

For the first time since the trial began, the courtroom at Fort Meade, Md., was full, and some spectators had to be accommodated in an overflow area where the proceeding could be watched on a live feed.

Manning has already pleaded guilty to lesser charges and faces up to 20 years in prison.

Prosecutors seek to have him convicted on the more serious charges of aiding and abetting the enemy and violating the Espionage Act. If convicted, he could be sentenced to life in prison.

Prosecutors rested their case last week after calling more than 80 witnesses. Defense lawyer David Coombs is expected to call nearly 30 witnesses.

Three military witnesses testified Monday about a lack of computer security at the forward operating base in Iraq where Manning worked.

Capt. Steven Lim, Manning’s superior, said it was standard procedure for analysts to copy information from the secure computer network onto CDs. Computers at the base constantly crashed, and to save work, many analysts saved intelligence products and other information to CDs. The prosecution sought to portray Manning as reckless for copying material onto CDs and said it was a violation of military procedure.