This grapheneOS may be another scheme from the 'deep FBI'/'services' to get intel on the very, VERY, nasty (terrorists, human traffickers, drug cartels, child stuff, etc). If I recall properly, they did that in the past (it seemed to have worked amazingly).
If so, "normal" police would not have the "keys". This would be "the compromise".
There are videos on youtube on the previous deep FBI/services hardware tech scheme.
In this context, grapheneos looks like more just 'And Another Time...'.
In the end, it does not matter: we all know here that "information system security" is a fantasy, it does not exist. When somebody does pretend the opposite: this person wants to scam you or sell you something.
If so, "normal" police would not have the "keys". This would be "the compromise".