Aside from the people shown depositing in several drop boxes, there is also the fact that no way could they be sure that it was the same people at different drop boxes, even with cameras. Dishonest people change clothing and do things on different nights in different places if they are smart about being dishonest people, aside from being morally stupid.
If it is the same cell phone it would be unreasonable to claim the same phone was used by multiple people.