Judge M L Villar made the ruling in Los Angeles County Superior Court after hearing testimony from police and watching videos that a prosecutor said showed the fatal beating of Xinran Ji.
Ji, 24, was hit with a bat during an attempted robbery July 24 as he walked to his off-campus apartment after a late-night study session. He ran from his attackers, but they caught him a block away and continued the beating until he was on his knees.
Deputy District Attorney John McKinney said the four were driving around looking for someone to rob when they saw Ji. One of the suspects said they targeted Ji because he looked Chinese, and they thought he would have money.
The killing renewed concerns about the safety of USC's Chinese students, who make up about 40 percent of the school's large foreign population.
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Video cameras in the area caught footage of Ji being surrounded by the teens and struck with a bat. A second camera showed him running around the corner and then being caught a second time, where he was seriously beaten.
A USC public safety officer's car can be seen on video passing the crime scene seconds after Ji managed to get up. He staggered home, trailing blood the whole way. His roommate found him dead in bed the next morning.
"He suffered the most significant brain injury, so it's hard to believe that his judgment wouldn't have been compromised at some level," said McKinney, who also suggested an alternate explanation.
"He was someone who extends a helping hand to others more than he seeks a helping hand. He may have been in a position where he thought he could take care of this himself.