Why are the police so bad at solving murders?

Thompson: This brings us to explanation No. 3: How much of this is about guns?

Asher: In the 1960s, about 50 percent of murders were committed with guns. Today, almost 80 percent of murders are committed with guns. And the share of murders committed by firearms has crept up at a nearly identical rate to the steady decline of murder clearances. Correlation does not equal causation, but if you plot the two together, you see a very strong correlation in the last 40 years.

And the reason is that firearm murders are much harder to solve. They take place from farther away. You often have fewer witnesses. There’s less physical evidence. There’s a great retired LAPD detective, John Skaggs, a character from the terrific book Ghettoside, who describes “ground-ball murders.” Like an easy ground ball in baseball, these are self-solvers. The police walk in and they find the husband with the bloody knife in his hand, and the spouse’s body is below him. The police don’t do anything to solve this; the case solves itself. Most of these self-solvers are non-firearm murders. So a higher share of gun violence can lead to a lower clearance rate.