It's not necessarily the case though that fewer crimes are being actually "solved," in the most precise sense of the term.
It could be that the current heightened interest in police oversight and focus on investigation of (and huge lawsuit payouts as a consequence of) wrongdoing by the police has made it less likely that people will be railroaded/framed for crimes they didn't actually commit, so the rate at which crimes are marked as solved has declined, even as the rate at which they actually are solved hasn't.