1 - I don't have a cite - I'm asking in case anyone wants to confirm or deny it - do you have a cite for this?
2 & 3 - There is, of course, a possibility that the alleged way SM was arrested had an effect - the fact is that the police felt that they needed to question him urgently, and pulled him in.
I think the suggestion might be that, if SM did have a history of sectioning himself, the cops maybe wanted to nab him quick.
1. I don’t have a cite and tbh it’s the first time I’ve heard the claim. Can I ask where you heard it? Was it locally?
2&3 The questions asked of SM suggest that they did not see him as an imminent threat and that fact that he was questioned, or should have been, with regard to perverting the course of justice and not murder further suggests this.
I would agree with your last sentence, if his mental health history had suggested a violent element. Did it?
That DF seems to have set great store on the aggressive way SM was arrested tends to suggest that there was no justification for it.