Yes, why leave the bag and risk touch DNA or car fibers getting on the bag? Also, as I understand, dogs tracked the bag from a local school to the drop off point. Why risk lurking around the neighborhood late at night to drop the bag? It seems like he just didn't throw it out of the car window or whatever.
Why leave the bag at all? I get that maybe he wanted to throw off detectives in the opposite direction, but he could have done that with just leaving her water bottle or one specific item with her name on it. Why the whole bag, risking exposure?
It would seem odd too if the perp did not touch something in the bag. I mean, did he wear gloves when he handled the bag and its contents? If so that would indicate a very well, planned out attack and not something done as a crime of opportunity.
he could have easily discarded the bag in the trash somewhere or even burned its contents. He wanted the bag to be found but why? Maybe it is the case that the perp is nearby and wanted to throw off LE to get away from tne neighborhood?