Based on two weeks of reports, police have been arresting suspects in about 30 per cent of robberies committed in the District. (iStock) (iStock/iStock)

Sometimes, as is familiar to watchers of television series, crimes are solved by dogged investigation over many days. But recent crime reports from the D.C. police show that arrests often result from rapid response by officers.

The latest two of the weekly reports issued by D.C. police on robberies and arrests list 23 crimes in which arrests were made. According to the reports, arrests in 14 of the 23 robberies were made by officers who responded to the scene.

One possible conclusion is that, as is often suggested by law enforcement specialists, many robberies are crimes of impulse and opportunity. In these offenses robbers might not have planned how they will make their getaway.

As a result, police arriving quickly and using witness descriptions to begin searching may locate suspects before they have gotten far from the scene.

In an average week about 40 robberies have been reported in the District. Making arrests in 23 robberies over two weeks suggests a robbery arrest rate of about 30 per cent.

In one of the most recent of the robberies in last week’s police report, someone snatched cash from a victim’s hand at 11:40 a.m. on Wednesday in the area at Sixth and H streets NW, police said.

Police said a man in his 40s was “apprehended by responding ­officers.”

In an earlier incident, police said a BB gun was used in a 1 a.m. robbery July 20 in the U Street NW corridor.

Police said officers who responded to the robbery, which was reported in the 1000 block of U Street NW, made two arrests and found a BB gun.