(CNN) - Two people were killed and two others were wounded in a shooting outside Benito Juarez High School southwest of downtown Chicago Friday afternoon, Police Superintendent David Brown told reporters Friday.

No suspects are in custody, he told reporters at a news conference. Brown said he didn’t have any information about the victims – other than the two wounded victims are in serious condition – because the investigation is in its early stages.

Earlier Chicago Fire Department Spokesperson Larry Langford said four students were shot. Brown said he didn’t want to speculate and wouldn’t confirm the people shot were students.

The school was releasing students in staggered groups when the shooting occurred, Brown said.

The people were shot outside the school building, but on school grounds, Langford said. They were transported to Stroger Hospital.