Help regarding Ds and another boy at school, how to approach this?

[Tambaboy]

I find myself in a bit of a difficult situation regarding my ASD DS (6) and one of his friends at school. DS has been going to school with the same children since nursery and he has a few friends that are very tolerant of his ways, one of them even sticks up for my DS when other children are mean to him, calling him “weirdo” and the lot.
There is one boy in particular that DS has been having problems with, it all came to light just before half term. Now I'm not going to speculate whether he boy has any additional needs or not, it’s not my place so I can only go for what I see happening and what and my DS tells me. I’m in friendly terms with his mother but we are not friends. I know the school suggested she asked for a referral to see the developmental paed but she refused to do so as she didn't see the point to it, she told me so.

Up until now I have encouraged the friendship as this boy seems to have great affection for my DS. I heard from other parents that their DC had had trouble with this particular boy being violent but as I said he was nice to my DS albeit a bit rough.

But this last couple of weeks things have gotten a bit out of hand as this boy tried to smother my DS while on a (first) playdate at our house. That happened when left alone while I was feeding the pets.
On the last day of school before half term several boys from school went to play to one of DS’ friend’s house and I was there to help (and supervise). Ds was overwhelmed by it all and wanted time out and went upstairs for a quiet time. DS later told me this other boy threatened to kill him pushing him down the stairs because he didn’t want to play. Not only this but DS then proceeded to tell me how "mean" this boy had been towards him for the last few months at school. I don’t want to go into detail but the things my DS told me warrant a visit to the school and speak to CT for them to intervene.
I think this boy needs more support at school but how should I approach this? I don’t want to go guns blazing into the HT’s office but I really think it needs to get addressed. Do I speak to the mum? I don’t really know how to best deal with this.
Apologies for the length of the post. Any advice appreciated.

I wouldn't approach the mum... I would go see the CT and discuss your concerns and ask him/her to report back to you.

We had a situation at school, ds had come in from play and was agitated saying he didn't want to go outside. He refused to talk about why.

Eventually he did and it transpired that a boy in ds's class (reception YR) had told him that his granny had a big sword and he was going to chop ds up into little pieces and put him in a stew! With his literal thinking ds believed every word of it. Where he got this type of language from is another matter entirely.

CT handled it very well and the boy in question was sanctioned.

Thank you very much for your replies, I'll arrange a meeting with CT next week. I had the feeling talking to the mum would have been a bad idea and you both have just confirmed it. Thanks