SAN ANTONIO -

A jury is deliberating in the case of a Lackland Air Force Base instructor accused of preying on female trainees in a broad military sex abuse scandal.

Closing arguments in Staff Sgt. Luis Walker's trial were held Friday.

Prosecutor Maj. Patricia Gruen called Walker a "wolf in sheep's clothing" who took advantage of already scared trainees. But Walker's attorney, Joseph Esparza, argued authorities have offered no other evidence besides the testimony of alleged victims to back up their case.

Walker is charged with 28 counts, including rape and aggravated sexual assault involving at least 10 women in basic training.

His trial is seen as the cornerstone of a major investigation into trainers at Lackland, where every American airman receives basic training.