LOS ANGELES—A 19-year-old USC student who confronted and fatally stabbed a man he witnessed breaking into cars near the university’s Greek Row will not face any criminal charges, the District Attorney’s Office announced Thursday.

“After careful consideration and a thorough review of all available evidence, we have decided not to pursue charges against USC student Ivan Gallegos,” District Attorney George Gascón said in a statement. “We believe that Mr. Gallegos’ actions were driven by a genuine fear for his life and the lives of others. Our heart goes out to the deceased’s family, friends and everyone impacted by this tragic incident.”

Mr. Gallegos had been jailed on suspicion of murder for the stabbing of Xavier Cerf, 27, who was pronounced dead at the scene around 8:15 p.m. Monday in the 700 block of West 28th Street, east of University Avenue.

Mr. Gallegos was released from custody at 12:22 p.m. Thursday, according to jail records.

LAPD interim Chief Dominic Choi told the Police Commission Tuesday morning that Mr. Gallegos confronted Mr. Cerf, who was breaking into vehicles. Mr. Cerf allegedly told Mr. Gallegos he had a gun, resulting in the student stabbing him, Mr. Choi said.

Mr. Cerf tried to run away through an alley, where responding officers eventually found him suffering from multiple stab wounds, according to Mr. Choi. Several witnesses described seeing a pool of blood near a fraternity house.

According to the LAPD, two other men who were with Mr. Gallegos when he confronted Mr. Cerf were questioned and released at the scene.