(CNN) -- The U.S. Air Force has now identified at least 31 women as victims in a growing sex scandal, a four-star general said Thursday, and there might be more. The Air Force is broadening its investigation to "actively seek any others that may have been affected by this," Gen. Edward Rice, the commander of Air Force Training, said.
"We are taking a comprehensive look not only at the cases that we know, but trying to do the best we can to assess whether or not there are other cases out there," Rice told reporters at the Pentagon.
Rice said the Air Force had taken "the unprecedented step" of shutting down all recruit training for one day to give a written survey to all basic military trainees at Lackland Air Force base. The Texas base has become the focal point of the growing scandal.
One trainer has pleaded guilty to having an improper relationship with a trainee, as part of a plea agreement.
Staff Sgt. Peter Vega-Maldonado has been sentenced to 90 days in prison, 30 days hard labor and a demotion in rank and pay. In his plea deal, he also provided testimony against two other trainers who have been charged. He also said he had inappropriate relationships with 10 trainees.
The scandal came to light in June 2011, when a young female trainee came forward and accused her male instructor of assaulting her. Staff Sgt. Luis Walker now faces a general court-martial on 28 charges, including rape, adultery and aggravated sexual assault. He is scheduled to appear in court July 16.
In November 2011, Rice says several military training instructors, both men and women, overheard a group of male instructors "talking about incidents that were unacceptable" and reported what they heard to superior officers.
This week, the Air Force brought charges against two more instructors.
Master Sgt. Jamey Crawford is accused of giving alcohol to a female trainee and having sex with her. Tech. Sgt. Christopher Smith is accused of seeking to conduct an intimate relationship with a trainee, making sexual advances toward a trainee and carrying on a personal social relationship with a second trainee.
"The basic training environment in particular is a target-rich environment for sexual predators," says Anu Bhagwati, a former Marine Corps officer who says the problem goes beyond one branch of service. Bhagwati says there's no such thing as male instructors having consensual sex with young, female recruits.
"You cannot do anything without requesting permission from your drill instructor. You cannot use the bathroom, you cannot move from left to right, you are literally in many cases a robot waiting for permission to take a step. And if you have that relationship which is based on fear and intimidation ... if that's the person you're asking help from, it becomes a very bizarre scenario."
Bhagwati was a communications officer and martial arts instructor in the Marine Corps, and she said she witnessed several incidents of sexual harassment of junior female Marines.
"You are subject to every single order that comes out of that instructor's mouth. If you're not going to tell him, who are you supposed to tell? And how are you supposed to get out of that unit to seek help?"
Rice agrees. "Personal relationships of any kind between trainees and instructors is strictly prohibited by our regulations and our instructions."
Rice said he does not believe the investigation of 12 instructors at Lackland necessarily means a systemic problem exists across the entire Air Force training command.
"Nine of those 12 were in one unit. We have a total of nine squadrons, and nine of them came from one squadron. So in my assessment to this point, it is not an issue of an endemic problem throughout basic military training. It is more localized."
The Air Force has relieved the officer who commanded the 331st Training Sqaudron during the time these incidents took place. He no longer runs the squadron, but "remains in the Air Force, in 'administrative hold' at Lackland Air Base, pending his next assignment," Rice said.
The Air Force said 11% of its military training instructors are women. In response to a question from CNN, Rice said, "I will look at whether we need to hire more female MTIs, and whether we need to have only female MTIs over female trainees."
The Pentagon estimates 19,000 sexual assaults occur each year. But only 14% of these crimes are actually reported. And less than 8% go to a court-martial.
Defense officials say every base is supposed to have a confidential sexual assault response coordinator.
Defense Secretary Leon Panetta recently announced special victims units would deploy trained professionals to various bases around the world. These independent personnel would be trained in interviewing victims and collecting evidence of sexual assaults.