How awful for your son. I hope he is ok now.
We had a similar case here in Pgh where two gang bangers who were still in high school attacked a guy with a concrete block and stole his phone. Fortunately, they were so dumb they used it to upload photos of themselves in the HS, and the victim was able to see this through his photo account somehow. That’s how the cops tracked them down.
Most devices allow all photos to be linked to all devices. I have to point that out to my clients when they send their children to the other parent with a tablet, phone, etc. No privacy unless you ask for it.