TACOMA, Wash. -- Pierce County prosecutors have charged three male teens, ages 13, 14 and 17, with second-degree rape and assault for allegedly sexually assaulting a 15-year-old girl at her home, then posting photos of the attack on social media.

The two younger boys pleaded not guilty in Juvenile Court last week. A hearing is set to determine whether the 17-year-old will be tried as an adult.

“Our community is shocked,” said Prosecutor Mark Lindquist. “The investigation is ongoing and there will be full accountability.”

On March 13, prosecutors say the victim, her sister and several boys were hanging out in a shed at the girl's home in Lakebay. The girl drank "a significant amount of alcohol and passed out in the shed." While she was unconscious, the teenage boys sexually assaulted her, tied her ankles with a hair straightening cord and dragged her around the shed.

The victim's 14-year-old sister was in the shed during the attack and tried to protect her, say prosecutors.

In the morning, the victim's mother found her passed in the shed, bloodied and wearing only a t-shirt. She was taken to a hospital and treated for her injuries.

Multiple witnesses told police they received photos and partial videos of the alleged attack on Snapchat, an app that deletes photos once it is viewed by the recipient.

Detectives are continuing their investigation into the incident.