SAN ANTONIO -- Military officials say the initial flirtations that Staff Sgt. Luis Walker directed at the women he trained at a Texas Air Force base became something more sinister: threats and intimidation that led to sex and eventually rape.
Walker is among 12 instructors at Lackland Air Force Base in San Antonio who are being investigated in a widening sex scandal that has rocked one of the nation's busiest military training centers.
Walker's court-martial is scheduled to begin Monday.
He faces the most serious charges in the case -- 28 counts, including rape, aggravated sexual contact and multiple counts of aggravated sexual assault. He could get up to life in prison and a dishonorable discharge if convicted.
The 10 female recruits Walker is accused of either sexually assaulting or engaging in inappropriate sexual conduct with are expected to testify during the court-martial at Lackland. A seven-member jury made up of military personnel will decide the case.
At least 31 female trainees have been identified as victims in the sex scandal.
Officials at Lackland are calling Walker's court-martial the "cornerstone case" in the ongoing investigation.
"We haven't had a case of this magnitude, certainly in recent memory," said Brent Boller, a spokesman for Joint Base San Antonio, which operates Lackland.
Walker's civilian attorney, Joseph Esparza, declined to comment.
The start of the court-martial Monday is expected to mostly deal with procedural matters. Testimony in the case is not likely to begin until Tuesday.
The sexual misconduct at the base apparently began in 2009, but the first woman didn't come forward until last year. The first allegations were levied against Walker, who is accused of crimes that allegedly took place between October 2010 and January 2011.
According to the Air Force charge sheet, Walker had sexual intercourse with 4 of the 10 female recruits. He also is accused of making flirtatious or sexually suggestive comments, sending inappropriate text messages and sometimes groping his recruits.
Walker also is accused of telling one recruit to "get naked" and that she "turned him on," forcing five recruits to engage in sexual acts by threatening their military careers and intimidating two of the women into lying about his alleged misconduct, according to the charge sheet.
Walker was a trainer for about 18 months, until he was removed from his position in June 2011. He joined the Air Force in 2004 and previously was stationed at Dover Air Force Base in Delaware and at facilities in Montana and Korea. The Air Force is withholding his age and hometown.
Lackland is where every American airman reports for basic training -- about 35,000 a year. About one in five is female, pushed through eight weeks of basic training by a flight of instructors that are about 90 percent male.
Six of the 12 instructors under investigation for misconduct face charges ranging from rape to adultery. Officials say nine of those instructors were in the same squadron.
The first court-martial in the case resulted in a plea agreement in June, when Staff Sgt. Peter Vega-Maldonado admitted to having sex with a female trainee. He struck a plea deal for 90 days confinement. He later acknowledged being involved with a total of 10 trainees -- a number previously unknown to investigators.