The confiscation of the phone may not show anything. To my knowledge, there's no electronic trail of what's done on the phone if it does not involve communications. The way flash memory works is that there's no way to figure out whether something was recorded and deleted or if no recording was made in the first place. And if something was deleted, there's no way to find out who did it or when.
If there was nothing amiss, why confiscate the phones?
You can’t possibly be so ignorant as to think the cops were not attempting to obstruct justice.
I have first-hand knowledge.
Android phones at least for some reason keep hidden files of the group of thumbnails created every time you decide you want to look at pictures and video. This would show at least that there was some kind of movie there.
As to flash memory, it's invariably treated like a DOS hard drive, and the same tools you can use to (sometimes) recover "deleted" files from a DOS hard drive can be used on USB flash drives and the flash memory in a phone as well.
A second strategy for recovering something stored and deleted would be to try to recover the file at the level that the flash memory controller wrote it, not at the level that DOS wrote it. That would be very specialized work to be done by the manufacturer.
Liberal boy, show cause for confiscating the phones of bystanders.
I am not interested in the police state you personally espouse.