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DES MOINES, Iowa — One person was killed and two others were critically wounded Monday after gunfire that appeared to come from a passing vehicle struck them outside an Iowa school, authorities said.

Des Moines police said in a news release that potential suspects have been detained in the shooting on the grounds of East High School, near Des Moines’ downtown, about a half mile, from the Capitol. No charges were immediately filed.

Sgt. Paul Parizek told KCCI-TV that calls started pouring in around 2:50 p.m., shortly before classes were scheduled to dismiss for the day. The district said in a series of tweets that the school was initially locked down but later it announced that students were being allowed to go home.

Parizek said he didn’t know whether the victims, who all appeared to be teenagers, were students. Their names weren’t immediately released.

“It is a punch in the gut that we have three kids in the hospital,” he said, “but we are hoping for the best for them.”

Police said they do not believe there is a continued threat to the public.

“It is sad but we do train for this,” Parizek said. “We do have to be prepared for it and this is why.”

A motive was not immediately known, and Parizek provided no details on the potential suspects. Authorities have recovered shell casings from the scene as they investigate what happened.

“Obviously, we threw every resource we had at this. We know that the kids in that school are our community’s most precious cargo.”