The shooter attempted to gain access to a locked-down classroom by telling students he was with the Sheriff's department. The students weren't buying it.

Law enforcement officials in the suburban Detroit city are crediting Active Shooter training at Oxford High School for keeping Tuesday's death toll low.

Three people were killed and as many as eight injured in the shooting, which took place during classes Tuesday.

The training had students shelter in place in their locked classrooms to keep the shooter at bay.

In this chilling video posted by an Oxford High student, the gunman tries to infiltrate a classroom by pretending to be a cop . . . but the kids knew something was up when he used the word "bro."

We grabbed calculators, we grabbed scissors just in case the shooter got in and we had to attack them,' senior Aiden Page told CNN.  Page also told them he thought one bullet had penetrated a desk used to barricade the door. It was not clear if Page was in the classroom shown in the video.

Using desks as barricades and locking down rooms are all part of the Active Shooter training students had gone through prior to Tuesday's incident. They also used that training to escape out the windows after this encounter.

Three people were killed, and they were identified Tuesday night by police as Hana St. Juliana, 14; Tate Myre, 16, and Madisyn Baldwin, 17. Another eight people were injured - seven students and one teacher, according to the Oakland County Sheriff's Office.

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