But in the 15 months since Mr. Diallo's death, gun seizures have slowed down, with only 105 arrests.

Police officials have theorized that the decline in gun seizures may partly be the reason for the increase.

But its gun seizures have plummeted by 40 percent this year, compared with the same period last year.

Since 1997, the unit, which patrols for violent criminals carrying weapons, has accounted for nearly 40 percent of all gun seizures.

"I see a correlation between the decrease in gun seizures and the increase in shooting incidents," Mr. Norris said.

Its gun seizures have declined.

Other usual barometers of falling crime, such as gun seizures and arrests of all sorts, have increased in recent months.

Mr. Safir reversed his decision two months ago, allowing some of the officers to go back into plainclothes after overall gun seizures began plummeting.

Members muttered about maintaining quotas on gun seizures and arrests, particularly when crime was at its lowest rate in decades.

Criminal justice experts are not always sure how to interpret an increase in gun seizures.