She was 8 months pregnant & as I understand it, they broke up a few months ago. So there's a chance that it's his child that passed, which adds an additional layer of motive. That being said, he looks to have not physically done it (like Rae Carruth) & wasn't even technically in town. He could of hired someone but that usually takes money, which he hasn't gotten yet. I would think the police would check his bank accounts & see if any large sums of cash had been withdrawn / major money moments. Following the money is usually a good start, then talking with all their mutually friends.
Personally speaking, I think the dude got railroaded & she got herself in a street debt figuring she'd pay it off when the contract was signed. When the money guy found out she couldn't pay, he made an example out of her not to borrow unless you can pay.