Detroit police at the scene of a murder. REUTERS/Rebecca About one third of all murders in the US go unsolved, according to a segment Monday morning on NPR.

Today, the national "clearance rate" for murders, which means the case ends in an arrest, is 64.1%. Five decades ago, it was above 90%.

This statistic means that 200,000 murders have gone unsolved since 1960, NPR noted.

NPR identified some potential causes for the depressing decline: