In the fantastic book Ghettoside about gun violence in america, the "protagonist" of the book, an LAPD detective, argues that a 30% clearance rate is actually even worse than it looks. He classes ~30% of murders as "self solvers" - murders that don't require much, if any, investigating to solve. Stuff like murder-suicides, cases where the shooting happened in front of a cop, cases where the killer walked into the police station to confess. A clearance rate of 30-40% in practice means that only a few murders beyond those self-solvers are actually getting solved

The book also discusses how low clearance rates create low clearance rates - instead of expecting the state to solve the murder of their friends/family, individuals instead take vigilante justice into their own hands, but this reality just creates cycles of violence and leads to accidental killing of bystanders and misidentified people

Can't recommend the book enough - though it's depressing because it was written in the first half of this decade when murders were steeply declining nationwide, and concludes on an optimistic note. Whereas now nationally we're at levels we haven't seen since the 90s