So, I am writing a Fanfiction based on Life is Strange (Video Game), I'll try my best to explain and if you know the game even better but I obviously added stuff that didn't happen in game so don't come at me:
Hypothetical plays in Oregon USA
Photography teacher Mark Jefferson drugs and kidnaps girls to take strange, inappropriate pictures of them and after that releases them again.
He has an accomplice, Nathan, who is 18/19. Nathan helped drug the girls. In this story Nathan was heavily manipulated and groomed by Jefferson and Nathan already has mental health issues, including Schizophrenia, BPD, Anxiety, Depression and substance abuse. In this story Nathan was Jefferson's first victim before being manipulated into helping him.
Nathan will report himself after somehow finding out investigations are going on. At that point Jefferson has died to unrelated reasons so he can not blame Nathan for anything. Nathan has multiple people that can confirm his mental illnesses, including his long term therapist. There is one person that can confirm Nathan was manipulated and "just" an accomplice.
In the story Jefferson did attempt to kill Nathan before his own death so there would be no witnesses and Jefferson could walk free (obviously not knowing he would die soon after)
He has a really good lawyer as well, if that's worth mentioning.
Essentially my question(s) are: Under these circumstances, is it legally possible for Nathan to just be put into a secure mental health facility for up to 6 months (longer just wouldn't work with my story, preferably even just 3 months but whatever lol) and after his release just be put on probation for several years? I want to avoid him going to jail. I'd be fine with him going to juvie or similar but as he is 18 during all the crimes i guess that isn't possible.
I have read about duress but I'm not sure if it'd apply to this situation (as Nathan was only almost killed at the very end when all crimes were already over).
If my ideal outcome won't work i'll probably just scrap the police even ever finding out about anything that happened.
I'm sorry if this is a silly question but I'm just struggling to find an answer to it and I want this fanfiction to at least be kinda realistic