A military judge, Col. Denise Lind, will decide the case without a jury, a procedure requested by Manning, USA Today reported.
Manning, 25, could spend the rest of his life behind bars if Lind finds him guilty of espionage and aiding the enemy. Manning has acknowledged leaking thousands of classified documents to Wikileaks.
David Coombs, a lawyer and lieutenant colonel in the Army Reserve representing Manning, said the Army private first class was not "seeking attention" when he leaked the material. He cited emails Manning sent in 2009 just before he was deployed to Iraq, where he served as a classified intelligence analyst, and just before his arrest.
"I'm more concerned about making sure that everyone, soldiers, Marines, contractors, even the local nationals, get home to their families," Manning said in one.
Coombs said the messages give Manning's motive for his actions. Manning had no interest in aiding al-Qaida or releasing information that could harm the U.S. military, he said.
"That is a whistle-blower. That is somebody who wants to inform the American public," Coombs said.
Lind chided Manning supporters who applauded when Coombs finished.
Maj. Ashenden Fein, the military prosecutor who gave his closing argument Thursday, responded to Coombs with a rebuttal, saying once again Manning was not a whistle-blower: "This is a soldier who knew exactly what he was doing. It was against the rules and against his oath."