They suspected him for terrorism based on? Because to do a lawful and reasonable search they need a reasonThey suspected him of terrorism - and they were looking for anything incriminating…
Ok, let me try to simplify… the authorities aren’t complete fools. If a phone had the option to “restore to something that looks like an inoffensive phone”, they would know about it - and be able to look beyond. Unless the data is irretrievably lost, they WILL find it.
Also, yes, cops are stupid sometimes, and almost always when it's a non soecialised cop when it comes to security technology, so if it makes it irretrievable, which I'm decently sure it does in Graphene's case, probably lost (HENCE why procedures exist and an officer shouldn't be doing this out of nowhere on the field)