Either the bomb was done by the man or by someone else. If it was done by someone else it wasn't a good way to rob a bank. The man could lead them back to the bad guy too easily. So, if it wasn't for robbing the bank it was done to make a statement or out of pure sadistic tendencies. No statement was reported so if it was done by someone else it was for pure evil sadistic pleasure and its likely such an animal will strike again.
The second possibility is it was done by the man himself. If the man wanted to commit suicide he may have had a reason to hide it. Reasons to hide it could be financial or emotional. He may not have wanted a friend or family member to know or he may have wanted to a suicide to look like a murder for insurance purposes.
If I had to place a bet my bet would be that the man had a suicide pact with the other worker but wanted to make his death appear to be from a murder and not a suicide. I would look to recent insurance policies and whether these two guys had aids or something.
AIDS ain't the death sentence it once was. With drug cocktails, some people have been able to keep it at bay.
It is odd the other fellow killed himself, however, this could be anything from general psyche trauma to they were gay and the senseless death of his lover pushed (the other) him over the edge.
All speculation at this point.
But I did see it mentioned the victim had three cats.
I wonder what their role in this was????