Active Shooter Drill at School in Loudoun County

A school surrounded by police cars and emergency vehicles is a sight no one wants to see, but the Loudoun County Sheriff's Office surrounded Loudoun Valley High School in Purcellville Monday morning to test its ability to deal with an armed intruder.

The sheriff's office took advantage of a teacher work day to stage a first-of-its-kind drill for the county: More than 70 teachers were present while the mock attack was staged. The scenario involved a gunman who burst into the school through a door left open for faculty. A teacher called 911 and a lockdown was ordered as shots were fired and deputies rushed to the scene. Within five minutes, the gunman was confined to a classroom where he shot himself in the head.

But in the staged incident, three teachers were also killed and nine were wounded. And the chaos didn't end there. Deputies soon learned the gunman had placed booby-trapped explosives throughout the school.

Sheriff Mike Chapman said his office and school officials began discussions about improving security soon after the December massacre at Sandy Hook Elementary in Newtown, Conn.

"We've never had a coordinated effort involving so many agencies as it would happen in real life," Sheriff Chapman said. "The key is to get out in front of this and do it in the situation where we can really prepare and make sure we're doing it right."

Loudoun County Public Schools Deputy Superintendent Ned Waterhouse was inside the school observing as the man portraying the shooter walked through hallways firing.

"Your adrenalin level went from 0 to 60," he said.

Waterhouse said the drill involving teachers is an essential step as the school district continues to tweak its security plan.

"What I saw today suggests to me it's no small feat to respond to an event of this magnitude, this gravity, and I as a citizens want our law enforcement to be as ready as possible," he said.

Sheriff Chapman said hours of debriefing with teachers and deputies would follow the drill. He said he'd like to schedule drills like this more in the future.