A Corvallis, Ore., teenager was arrested after a surveillance camera captured him preparing to sexually abuse a horse inside a barn, police said.

The owners of the barn installed the camera after reporting an assault on the horse last summer. In February, the owners noticed the halter of their mare had been moved, as well as some food dishes. When they checked the video, they saw a young man sexually assaulting the horse.

Deputy Clay Stephens of the Benton County Sheriff’s Office, who watched the video, said the youth, who was not be identified, seemed to be following a “very concise, deliberate, well-thought-out plan.”

The owners then installed a silent alarm. On June 7, at around 2:30 a.m., the alarm sounded in the house. The owners looked at the video monitor and saw the suspect preparing to assault the horse. They called the sheriff’s office and the 17-year-old was arrested at the barn