BILOXI -- A law enforcement officer needs a bulletproof mind to endure the psychological effects of dealing with aggressive persons and deadly situations, retired Army Lt. Col. Dave Grossman said Tuesday at the Biloxi Community Center.

"If you have a bulletproof mind, you can walk into the heart of darkness and walk out unscathed," Grossman said.

His audience was about 250 South Mississippi law enforcement officers and military personnel.

Grossman, an expert in the psychology of conflict, is a former Army Ranger, paratrooper and West Point psychology professor.

He founded the field of "killology" -- the study of the psychology of killing -- and is the author of three nonfiction books.

An officer also needs a warrior spirit, empathy and a willingness to kill to protect innocent lives, Grossman said, pointing to the threat of terrorist acts, including gunfire in schools. The training included dealing with potentially deadly school shootings.

"We must step away from denial and embrace preparation," Grossman said. "Fire drills in schools are not enough."

Grossman said understanding the psychological effects of police work can help prevent post-traumatic stress disorder or suicides.

Local police officials were already familiar with Grossman's expertise.

"For several years, if we have a potential member for our SWAT team, we put them through 'the Grossman drill,'" Gulfport Deputy Police Chief Chris Loposser said of a simulated shooting scenario with gunfire and screams.

U.S. Attorney Gregory K. Davis said his office helped sponsor the training because it is a valuable resource for police.

Other sponsors were the Biloxi Police Department, Mississippi National Guard, Mississippi Center for Police and Sheriffs, Regional Counterdrug Training Academy, Gulf Coast High Intensity Drug Trafficking Area program, Holmes Community College Police Department and the Mississippi Department of Education.