A confrontation between cops and teenagers kicked off the horrifying Baltimore riots

On Monday afternoon, before Baltimore's worst riots in over 45 years, more than 200 cops convened outside the Mondawmin Mall, the city's police commissioner told reporters late Monday night.

The police arrived at the mall before school got out. Somewhere between 75 and 100 people who "appeared to be high school students" began hurling bricks and stones at the officers, Commissioner Anthony Batts said.

"A number of them came out of the local high school on the other side of Mondawmin," Batts said late Monday, in the wake of rioting that came the day of the funeral of Freddie Gray, a 25-year-old black man who died from a spinal cord injury sustained in police custody.

The police knew to go to the mall because of rumblings on social media about a so-called purge, a reference to a movie where crime is legalized for 12 hours, as The Baltimore Sun Reports.

That "purge" was to start at the 3 p.m. at the mall, which is a gathering place for area teens. Police arrived in riot gear, according to the Sun. The students started pelting the cops, and the officers threw rocks back and sprayed tear gas, according to the Sun.

Vaughn De Vaughn, a local teacher watched the entire thing.

"This is about anger and frustration and them not knowing how to express it," he told the Sun.

By Monday evening, 15 police officers had been injured and many buildings had been looted and set ablaze - including a senior center that was under construction. On Monday, the governor of Maryland also declared a state of emergency and called in the National Guard.