The effect of police response time on crime detection

Police agencies devote vast resources to minimising the time that it takes them to attend the scene of a crime. Despite this, the long-standing consensus is that police response time has no meaningful effect on the likelihood of catching offenders. We revisit this question using a uniquely rich dataset from the Greater Manchester Police. To identify causal effects, we exploit discontinuities in distance to the response station across locations next to each other, but on different sides of division boundaries. Contrary to previous evidence, we find large and strongly significant effects: in our preferred estimate, a 10% increase in response time leads to a 4.6 percentage points decrease in the likelihood of detection. A faster response time also decreases the number of days that it takes for the police to detect a crime, conditional on eventual detection. We find stronger effects for thefts than for violent offenses, although the effects are large for every type of crime. We identify the higher likelihood that a suspect will be named by a victim or witness as an important mechanism though which response time makes a difference.