This is a good and interesting plot, but the premise doesn't sit well with me. Mostly because it turns the wife into a sort of psychopath. After all, if both of them are dead who would look after her child? If she cared at all for either of them the plot seems to fall apart. It would make more sense to me if the assassinations were keyed off of some sort of action on his part, like getting remarried. This would also turn the new wife into the prime suspect, as he would have inhereted a good deal of money from his previous wife. No one expects a dead killer.