By Sheena Jones, Steve Almasy & Darran Simon From CNN

(CNN)At least seven, possibly eight victims were injured Tuesday in a shooting at a school in suburban Denver, authorities said.Douglas County Under sheriff Holly Nicholson-Kluth said two suspects are in custody in the shooting at the STEM School Highlands Ranch, which covers K-12.Nicholson-Kluth said she believed the victims were injured by gunfire.The shooting started in the middle school just before 2 p.m., Nicholson-Kluth said. A school official called authorities to report that shots were fired, she said.”Over the next few minutes, quite a few shots were fired,” she said.

Officers heard gunshots as they arrived, undersheriff says

Police and sheriff’s deputies were on scene almost immediately, she said.”As officers were arriving at the school they could still hear gunshots,” Nicholson-Kluth said.

A community grieves after a mass shooting at the STEM School Highlands Ranch.Nicholson-Kluth said authorities don’t know at this point if the suspected shooters are students.Though authorities initially said they were looking for a possible third suspect, Nicholson-Kluth said they are no longer looking for another suspect.

At least three local hospitals were treating eight patients after the shooting.Five patients were being treated at Littleton Adventist Hospital in Littleton, hospital spokeswoman Wendy Forbes told CNN in an email.One victim was in good condition at Children’s Hospital Colorado South Campus in Highlands Ranch, according to Jaime Berg, a spokeswoman.Two juvenile patients were being treated at the Sky Ridge Medical Center in Lone Tree.

The STEM School was placed on lockdown after the shooting, the Douglas County School District said in a tweet. All other Highlands Ranch schools were on a lockout, the tweet said.The lockout was later lifted from Highlands Ranch schools, the district said.”This is a good community. It’s usually very quiet, extremely low crime rate,” said the undersheriff, who has been with the department 30 years.The STEM School has about 1,800 students, the undersheriff said. It is located about seven miles from Columbine High School, which is in Littleton, Colorado.On April 20, 1999, two students killed 12 of their classmates and one teacher in a mass shooting at Columbine High.Douglas County Schools were closed April 17 as authorities scrambled to find an armed Florida teen they said was infatuated with the Columbine massacre. The woman, authorities said, made threats before she traveled to Colorado, where she died of a self-inflicted gunshot wound.

CNN’s Chris Boyette and Michael Nedelman contributed to this story.

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