A former Joint Base Elmendorf-Richardson soldier and serial child sex offender has been sentenced for targeting teenage girls on social media and sneaking them onto base for sex.

Robert Walls, 28, was sentenced by U.S. District Judge Sharon Gleason Tuesday for coercion and enticement of three minors in Anchorage. He faces 15 years in federal prison, followed by a life term of supervised release, according to a release from U.S. Attorney for the District of Alaska Bryan Schroder's office.

Walls was indicted for his crimes in July 2018. According to the release, he was enlisted in the U.S. Army and stationed at JBER at the time. He was also reportedly aware of the Anchorage Police Department's investigation into him, which the release states continued after police searched his barracks.

An investigation uncovered that Walls, while living on base, used social media to meet and groom girls ages 14 through 16 for "the purpose of engaging in sexual activity" in the winter of 2017 through the spring of 2018. According to the release, this included the production of child pornography.

"Walls admitted to his conduct in regards to three identified victims, but social media account searches exposed several additional potential victims whose indentity has not yet been established," the release states. "All unidentified victims are encouraged to contact APD."

The release states Walls lied about his aged to his victims to sexually exploit them. He got them on base by hiding them in his vehicle and sneaking them in through his first-floor bedroom window.

Police investigated Walls after one of his victims came forward when she learned of his true age, relationship with another minor and the possibility she had been exposed to a sexually transmitted infection.

The case was investigated by APD's Crimes Against Children Unit. It was prosecuted by Assistant U.S. Attorney Adam Alexander.

Copyright 2019 KTVA. All rights reserved.