Iranian Christians— there are quite a few expatriates in the US, and they are harassed from “home” by the shiiteheads in Iran— for the property they may still have back in country, like farmland.
But the motive in this weird crime is not clear.
Unlikely they were Christians: one of the kids was named “Ali.” Also, if they were Christians, the media would have reported it. The national US media, while reporting the crime, has yet to identify the victims and killer.