Weemer's attorney, Paul Hackett, said that then-Cpl. Weemer was trying to gain control of a situation that his sergeant had let deteriorate. He said Weemer killed the suspected insurgent when the man tried to grab his gun.
"This is a tragic story that represents the reality of war," said Hackett during his opening statement.
Prosecutor Capt. Nick Gannon, however, said that Weemer was one of three men who executed four prisoners who posed no threat.
"This is a case about following the rules and doing the right thing at the most important time," Gannon said during his opening statement.
Weemer, 26, is charged with unpremeditated murder and four counts of dereliction of duty for allegedly failing to adhere to the military's rules for handling prisoners.
He has pleaded not guilty.
Read more about the trial on our media partner's website, The North County Times.