I am so sorry. In the suicide support groups I attended with my daughter after my son in law committed suicide, what the therapist repeatedly told us is that looking for someone to blame, especially for parents of kids who commit this act, is very, very common. If there is no one to blame, they will blame the coroner, the police, someone will be the cause in their eyes. I also learned that for some people, suicide is always an option, they consider it as a life option and the thought becomes a reality for some.
It was very helpful to listen in these groups while we were going through our own despair and sorrow. It may be a help for your son to know that all of his feelings, especially the hard ones, the anger at the person for doing it, is a normal reaction. Otherwise he may not be able to express that anger, which is part of the healing. Having been down this road, it is not like anything else, it is not like a 'normal' death, it has ramifications which are unique and even if you simply read about it, there are a number of books you can get, it will really help all of you to understand that the feelings everyone is having are normal, healthy, appropriate.
I send you prayers, wishes for healing for everyone's heart to mend, warm and tender hugs wrapped around thank you, you, your family, the family of B, to all who are touched by this act. My heart so goes out to you............