A 19-year-old found dead in his Camp Pendleton barracks had been beaten to death by a fellow Marine, investigators say.
Lance Cpl. Mario Arias Jr., from Canoga Park, Calif., was attacked at the San Diego County base over the weekend, authorities said.
The air crew trainee, from Marine Light Attack Helicopter Training Squadron 303, Marine Aircraft Group 39, 3rd Marine Aircraft Wing, enlisted in August 2010.
The Naval Criminal Investigation Service said the suspect is being treated in a hospital for "significant injuries" sustained when he jumped from a third-floor balcony.
Ed Buice, spokesman for NCIS at its headquaters in Quantico, Va., told msnbc.com that neither the suspect's identity nor the hospital where he is being treated would be released until charges had been brought.
He said there was no deadline for those charges, and that the timescale would depend on the suspect's recovery. The exact cause of Arias' death has yet to be determined.
At Camp Pendleton, two sources told the North County Times that the suspect was apparently drinking when he was confronted by Arias about his alcohol use, causing the suspect to become enraged.
Maj. Carl B Redding Jr., spokesman for Arias' command, said the teenager had been awarded the National Defense Service Medal as is customary following completion of boot camp during times of conflict.
Arias' friends and former teachers told NBC San Diego that he enlisted after high school and that his sister was also a Marine.
Close friend Janelle Farkas told the channel Arias liked building robots and was part of the Northrop Grumman Explorer program.
“His sister was a Marine. He looked up to her, admired her and wanted to follow in her footsteps,” she said.
“He wanted to use his engineering and those skills in the armed forces,” said his former teacher, Valerie Olenick.
“A horrified reaction to the fact that such a nice kid had to have his life cut so short,” Olenick added.
This article includes reporting by The Associated Press, msnbc.com staff and NBC News.