Sheriff's deputies arrested him after finding his 19-year-old girlfriend severely beaten on Monday night in their apartment. Police say they did not find a weapon.
She was transported to a local hospital, where she later died.
Needham's brother said the 25-year-old has not been the same since returning from his second tour in Iraq.
"He's been no good since he got back, i'll be honest. I mean, he's my brother, we grew up in the crib together, I love him like no one else, and it's sad to know the person who means the most to me, to completely write them off because they're crazy, you know," he said.
"Yesterday she had given me a call and telling me that he grabbed her and choked her and what not. And, well, I said, 'You need to get out of there.' If I could have gone back tomorrow ... If I had known it would lead to this," said Erik Krecu, a friend of the victim.
The victim has no family in the area. Authorities are trying to contact relatives in Northern California to notify them of her death.
Eyewitness News reporters Sid Garcia and Eileen Frere contributed to this report.