Hi Gimme and welcome to Websleuths
Yep, your post made perfect sense. I do think this could be what had happened. Mix a bit of truth into the lies.
If he had lost anything else, chances are he would have used his phone torch to search with. So the fact that he had to take a torch with him, could indicate it was the phone he was looking for. Plus, he was running as he left, which might have meant he needed to go all the way back to the crime scene, rather than just searching around his own garden/house.