As I've read through this thread something jumped out at me. The church has stressed the importance of two-deep leadership in organizations from Primary to Young Women and Young Men. Why hasn't this been implemented in Seminary? Just wondering
Anyway, getting back to your situation, speak with your Stake President or Bishop. If they try to sweep it under the rug, threaten to take it to the police. Or, if you feel inclined, skip the church leaders and go straight to the police. Think back to the horrible stories of young men being molested by Scout leaders and how some of those events were swept under the rug. Don't let this happen. You are the greatest advocate for your son.
Just an FYI, my son (now 16) was being bullied by another young man in our ward several years ago. I finally got fed up with it. Despite caution from ward members to not ruffle feathers, my attitude was, I don't care who I offend. It's my son and I'm protecting him. I called the boy's parents and met with them and their son and laid out the accusations. The boy has not laid a hand on my son since and my son tells me the boy doesn't like me. Quite frankly I don't care. I did what I had to do to protect my son because if I didn't, he said, among other things, that he wasn't going to go back to church.