Clearly this guy would have killed his ex in a heartbeat out of his blinding rage and desire for vengence. And she is a muslim.
He had kidnapped these kids and took them to Antigua & other parents for about a year, until he was located back in the states. The kids were removed from him and returned to the custodial parent, the ex-wife. She then disappeared, although he was trying to locate her (according to his lawyer who's been making the TV rounds); if he located her, you can bet he was stalking her. At least one of the theories was that one of the persons murdered was the actual target. It may be he hadn't gotten to her yet.
And if one parent dies, the other person almost always gets custody as the surviving parent.