SAN ANTONIO — Military officials say the initial flirtations that Staff Sergeant Luis Walker directed at the women he trained at a Texas Air Force base grew into something more sinister: threats and intimidation that eventually led to 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.
‘‘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 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.
His court-martial began Monday with a discussion of procedural issues. Walker’s father and two other family members were in the courtroom at the base.
A seven-member jury made up of military personnel will decide the case.
Ten female recruits are expected to testify. 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.
Walker’s civilian attorney, Joseph Esparza, declined to comment.
Major General Margaret H. Woodward has also launched a separate, independent investigation that military prosecutors say could implicate more airmen.
Advocates for female service members and members of Congress have started taking notice. ‘‘It’s a pretty big scandal the Air Force is having to deal with at this point,’’ Greg Jacob, a former Marine infantry officer and policy director of the Service Women’s Action Network, said last month. ‘‘It’s pretty substantial in its scope.’’
The sexual misconduct at the base allegedly 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 between October 2010 and January 2011.
According to the Air Force charge sheet, Walker had sexual intercourse with four 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.
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 staff of instructors that is about 90 percent male.
Six of the 12 instructors under investigation 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 Sergeant 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.