I am not an expert, but right now it seems like the police generally keep around your biometric data, but they don't keep it in a very useful way. I can't walk into the police station, show them a video clip on my phone of someone breaking into my car last night, they scan the video and it says "we found them, this is John Q. Smith". The data is on a piece of paper somewhere, or it's in a database that is rarely used for whatever reason. So in practice it's like they aren't storing it at all.

If the police did keep biometric data in a useful way, I think our society would have to be more explicit about what biometric data we want the police to keep. I don't know what the right answer is, but something like, if you are convicted by a crime then your biometric data is at least kept for a few years, that seems reasonable to me.