LOS ANGELES — Violence that sometimes borders the University of Southern California crept onto campus when an argument outside a Halloween party escalated to a shooting that critically wounded one man and injured three other people. The episode led administrators Thursday to reassess school policies.

Neither the victims nor the two men detained were USC students, but the shooting ­reinforced concerns that the campus’s location near downtown Los Angeles presents risks on and off campus. The shooting comes after security was strengthened after the April slayings of two graduate students near the school.