I'm re-reading all these posts and realizing that none of us really know enough about the details between the relationship between your husband, son, stepson, yet we are all throwing around advice like we are intimately involved and know all the history.
Please know that we are doing it because we want to give you love and support as you sort your way through this horrible experience. And of course, we are angry that a living being lost his life and worried about more trauma to you and yours.
That being said, I strongly advise you to seek professional legal, police/security and possible emotional support during this time of immense turmoil. This is not the time to be making decisions without proper counsel close to you and your situation.
Hugs to you, and know that the forum is here whenever you need to let loose.