The April 20, 1999 attacks at Columbine High School in Littleton, Colorado changed the way law enforcement responds to school shootings.

Crime Watch Daily Correspondent Jason Mattera got a rare look at how they train for these incidents. Mattera suited up with the Los Angeles County Sheriff's Department as they took part in an active-shooter training drill.

Cops no longer wait and watch. Now they move in immediately. And the L.A. County Sheriff's Department is leading the way with its Tactics and Survival Training Unit.

"Columbine was really a watershed event. Surround and contain while people are being shot and killed doesn't work," said L.A. County Sheriff's Tactics Instructor James Grady. "Time is life."

An "active shooter" situation is defined by the department as a gunman or gunmen killing or attempting to kill people in a confined populated area.

In the wake of Columbine, LASD has a bold new approach that requires special training, not only for its rank and file, but for potential victims. The Los Angeles County Sheriff's Department has formed a special Tactics and Survival Training Unit, and produced an instructional video for civilians.

"Even in the best cases, police are minutes, not seconds, away," the video informs.

"The tactics that we employ today, they're vastly different from the era of Columbine," said L.A. County Sheriff's Deputy Fernando Gonzalez. "Simply locking down a location and waiting for a special weapons team isn't going to cut it anymore."

Jason Mattera recently got a chance to take part in a basic training course with the department.