Prayers that someone finds her soon. IMO every inch of his place needs to be searched with a fine tooth comb and dogs. Every item examined, including coolers, buckets, boxes, vehicles, etc. Just because he left the store in the opposite direction from home, and was in that direction for an hour, doesn't mean Ember is in that direction. He could have brought her back.
Strange he won't say why he was gone an hour and where. He could have gone to see someone and left her in the truck. If it was an illegal reason, maybe no one would say.
If he took a curve too fast, or slammed on the breaks, Ember could have been seriously injured.
All that said, simplest thought, Ember was fussy and he couldn't calm her and lashed out, resulting in her death. Yes I realize many babies are violently murdered, but me heart doesn't want to think about it.
Friends need to think of routes in the area he knows and places he liked to hang out and search there.