I have no experience to draw on here but my vote is that yes, you go. I do not trust anyone else to do right by child until they have shown they have earned that trust. The courts, police and lawyers haven't had the opportunity to show you that, yet, so I think you need to be there. If for no other reason, but to assess the mindset and knowledge of those charged with dealing with your child. Odds aren't that good that they really know or understand a thing about ASD or the unique issues your child faces but maybe they'll be smart and access an expert ... you don't know until you go and see.
The tricky part is that your son is probably going to be emotionally upset seeing you, but you hold your line: you did not want to hurt him, and do not want to hurt him, but you could not allow him to hurt you and your husband, either.
You might want to consider bringing your own lawyer, too. The legal system is it's whole own animal, and sometimes everyone in a room can see what the fair answer should be, but still feel the law requires the opposite. A lawyer can filter that for you. And ... you may need that lawyer to take over your son's case.
It is incredibly unfortunate when things get to a point like this. I don"t think ANYONE has the answers on how to handle it and make it all better; it just isn't going to be "all better." Hard truth to swallow.
But, in the middle of all that, you're still mom. If it was my child, I'd want to be there. It's my job.
I guess that is the only part I really know: I'd want to be there.
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Mom to an amazing young adult AS son, plus an also amazing non-AS daughter. Most likely part of the "Broader Autism Phenotype" (some traits).