The fact that he has admitted it, should be commended. In my professional experience it is not that common for parents to own up to this, somewhat understandably, for fear of what they will lose. By admitting what he has done, the baby has presumably been able to stay living with it's mum (rather than been removed to another family to allow for many, many months of investigations), and the baby has been safeguarded from him. You don't know if this was a one off incident, if he snapped in the heat of the moment. It happens. He has admitted it and shown remorse. He is also suicidal. Poor mental health appears to be playing a role here, and that can be hugely complex. It is not so "black and white" as he has done wrong and should therefore be rejected by everyone.
Have you considered how your friend feels about what her son has done? She has potentially lost a relationship with her grandchild, and her son is now suicidal. She must be absolutely terrified that she could lose him too. Be careful of judging her, for her son's actions. She will be in pain. She will need your support. It's ok to tell her that you can't understand or support what he has done. I doubt she can either. But it sounds like she is going to need a friend who can be there, without judgment.
Have you considered how your friend feels about what her son has done? She has potentially lost a relationship with her grandchild, and her son is now suicidal. She must be absolutely terrified that she could lose him too. Be careful of judging her, for her son's actions. She will be in pain. She will need your support. It's ok to tell her that you can't understand or support what he has done. I doubt she can either. But it sounds like she is going to need a friend who can be there, without judgment.