Lance Cpl. Mario Arias, Jr., 19, from Canoga Park, was found dead in his barracks.
Investigators say another Marine attacked Arias, then jumped from a third-floor balcony. The Marine was seriously injured, but is expected to recover. His name was being withheld pending charges.
A motive for the beating has not been determined.
Arias was an air crew trainee from Marine Light Attack Helicopter Training Squadron 303 of the 3rd Marine Aircraft Wing. He had enlisted just last year.
A memorial service for Arias will be held this Friday at Canoga Park High.
The Associated Press contributed to this report.