Four teenagers were arrested in Thursday's deadly attack on a USC graduate student as he walked home from a study group, with police saying the incident was one of at least two robberies the group attempted that day.
Xinran Ji, a 24-year-old graduate student from China, was allegedly hit on the head with a baseball bat by at least one of the suspects, according to two law enforcement sources. Detectives are probing whether other weapons were also used, the sources said. The suspects range in age from 16 to 19.
"He was literally beaten to death," said LAPD Cmdr. Andrew Smith. "I don't know why a group of young people would go on a crime spree as terrible as this."
Two of the juveniles, a 17-year-old male and 16-year-old female, were also arrested on suspicion of murder, assault with a deadly weapon and robbery. Their names were not released by police.
Detectives said the 14-year-old was involved in Ji's assault "in some manner," Smith said, but that the "detail and depth of her involvement" was not clear.
Investigators are also trying to determine whether the suspects committed more crimes during Thursday night or early Friday morning, Smith said. Anyone with information about possible incidents were asked to contact police.
Ji's death sent fresh shock waves through USC, a community already sensitive to safety concerns after two Chinese graduate students were shot and killed in 2012 during a botched robbery just blocks away from campus.
Six months later, a man opened fire outside an on-campus Halloween party. Four people were wounded, though none were USC students.
After the 2012 incidents, USC and Los Angeles police amplified resources to the South L.A. campus. The university limited public access to the campus in the evening, the school's Department of Public Safety installed additional security cameras and license plate readers, and dorms introduced fingerprint scanners for entry.
About 1,500 feet of fencing also went up along the school's 2-mile perimeter, and security guards began checking identification cards of everyone coming inside after 9 p.m.
LAPD detectives are also embedded with campus public safety staff, he said, and the agencies attend each other's crime data meetings to stay up-to-date on what is affecting the university and surrounding area.
After the measures were implemented, property crime at the university was cut in half during overnight hours, according to statistics from the university and the LAPD.
Across all hours, violent crimes fell from 11 reported incidents in 2012 to four in 2013.