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Brennan Linsley, Associated Press
Police officers work in front of Skinner Middle School, where three juveniles, two with guns, the other with a smoke device, were arrested, in Denver, Friday, April 10, 2015. No one was injured, and the school was on lockdown for about an hour, police said.

DENVER — Three students — two found with handguns, the other with an unidentified device — were arrested Friday after causing a one-hour lockdown at a Denver middle school. No one was injured.

Students at Skinner Middle School reported the boys to school officials, who triggered the lockdown, police said.

Police Cmdr. Paul Pazen did not release any details about why the boys had the weapons, whether they had ammunition and where the guns were found.

At a news conference outside the school, Pazen praised other students for reporting suspicious activity.

"Our students are to be commended for seeing something and saying something right away," he said.

Several children said that they were told to go to the school auditorium and that the school was on lockdown. Once in the auditorium, students were told there was a youth with a gun, they said.

"We had so many drills I didn't know if it was a drill or not, but we took it seriously," said Maxcine Forsythe, 12. She said students kept as quiet as they could until they were given the all-clear.

"They just told us a student had brought a gun, and they wanted to keep us safe," said Mya Lucero, 12.

Her mother, Jessica Lucero, said she got a text from her daughter saying she was in the auditorium and wanted her mom.

"I had to get my baby. I just came," she said.

Denver schools security chief Michael Eaton said the school district conducts lockdown and lockout drills every semester.

"We train for this. Unfortunately, in today's world, we have to train for this in our schools," he said.

Police originally said one of the students had a smoke device. They later said they were still investigating what it was.

The school reopened for classes after the lockdown, but some parents arrived to take their children home. The scene was calm, with families periodically leaving the school along with police investigators.

One officer carried out a backpack in one hand and a paper bag in the other.