I only felt confused until I saw the neighbor who described how easily Jersey breaks into houses. This link, he tells a little of it, but I had seen a video of him on tv where he described Jersey's behavior at length.
http://fox4kc.com/2011/11/01/womans-cell-phone-confiscated-for-baby-lisa-investigation/
Since He was So clever at breaking into houses, and had such a long record of theft, it just seemed like "old Jersey" would be doing what comes naturally, and break into DB house when he saw them out front partying, even with kids inside, the adults were "distracted" and the adults were where he could keep an eye on them while he checked their home to see if there was anything he could sell. Then someone said, "but what motive?" I imagined myself as Jersey, I'm in the kitchen, I've got the phones, the baby starts making sounds like she is going to wake up.
Maybe he don't want to leave fast, maybe he knows of something more valuable he really needs to steal and sell. Then, maybe the kids have gone over to the neighbors. He tries to shush up the baby, and it is an accident. I just can't see anybody wanting to go kill a baby, especially the parents or other relatives.