EAST ST. LOUIS, Ill. -- An Air Force staffer stationed in Illinois pleaded guilty Wednesday to federal charges that he possessed pipe bombs that he told investigators he planned to unleash on local sex offenders to "inflict as many casualties as possible."

Justin Vangilder, 24, entered the pleas to three counts of possessing an unregistered destructive device. Each felony carries up to 10 years in prison, though Vangilder likely will receive less than that under federal guidelines when sentenced Aug. 1.

Vangilder was ordered to remain in custody, as he has since his arrest last October. At the time, he was assigned to Scott Air Force Base, just east of St. Louis, and was working as a communications specialist.

Court documents filed Wednesday in connection with his guilty pleas did not offer a possible reason for Vangilder's possession of the explosives. But an FBI agent's affidavit included in the criminal complaint said Vangilder had three pipe bombs in his home off base and told an informant that he fantasized about killing child molesters, seeking to "inflict as many casualties as possible."

There was no indication in FBI special agent Sanela Konjevic's affidavit that Vangilder targeted anyone on the base, where spokeswoman Karen Petitt said Wednesday the Air Force was ousting him from the service for "other-than-honorable conditions."

According to Konjevic's affidavit, the unnamed informant notified the Air Force's Office of Special Investigations after visiting Vangilder's Shiloh home and becoming alarmed by Vangilder's displaying of various pipe bombs in a briefcase, along with zippered plastic bags of shotgun shells, razors, screws and shrapnel.

The informant also said Vangilder called the explosives "a last resort," according to the affidavit.

"Vangilder then proceeded to explain to the [informant] his fantasies of killing child molesters and that he had detailed, personal information of sex offenders in the local area," Konjevic said in the affidavit.

Vangilder told the informant he was suicidal and disappointed that his parents didn't support him during his recent divorce, Konjevic added.

After his arrest, Vangilder underwent psychiatric evaluation and in February was found mentally fit to stand trial. On Wednesday, he told U.S. District Judge Michael Reagan he has been taking prescription medication for depression and post-traumatic stress disorder.