SAN ANTONIO (July 16, 2012)--The initial flirtations Staff Sgt. Luis Walker directed at women he trained at Lackland Air Force Base in Texas became something more sinister as they gave way to threats and intimidation that led to sex and eventually rape, military officials say.

Walker is among 12 instructors at Lackland Air Force Base in San Antonio being investigated in a widening sex scandal that has rocked one of the nation's busiest military training centers.

Walker, whose court-martial is set to begin Monday, faces the most serious charges in the case.

Walker is charged with 28 counts, including rape, aggravated sexual contact and multiple counts of aggravated sexual assault.

He could be sentenced to as much as life in prison and given a dishonorable discharge if convicted.