This is just awful. My thoughts are that it was some kind of random, unplanned crime. It sounds like the mother and the kidnapper had words for some reason. I think the kidnapper got angry and had a gun handy and shot the mother and then, for whatever reason, took the baby. I don't think this was planned out. How kills a mother and grabs a baby for trafficking in such a public place? And trafficking a baby isn't exactly a great way to make money. If they were after money then a robbery would have been more efficient and less likely to cause a huge manhunt like this is doing.
I hope their intention isn't to harm the baby but I highly doubt they took him because they wanted their own baby. These people are beyond heartless. Sadly I can see them doing something to the baby if they feel trapped.