CHICAGO (WLS) -- A security guard taken into custody after a woman was shot and killed at a nightclub in Stone Park Saturday night has been released, police said.

Family members spoke with ABC7 and said 21-year-old Zulma Daniela Calderon Pacheco was killed when a security guard fired a shot while trying to break up a fight.

The medical examiner has ruled the death a homicide.

The death happened around 2 a.m. Saturday at the Mansion Live Nightclub, 3801 W. Lake St., in Stone Park, officials said.