Seven narcotics investigators are convicted of planting drugs on people to meet arrest quotas. Eight current and former patrol officers are charged with smuggling guns into the state. Another is charged with making a false arrest, apparently as a favor for his cousin. Three more are convicted of robbing a perfume warehouse.

All these cases involved New York City police officers and unfolded or were resolved in recent months. But beyond the fact of criminal charges against those sworn to protect the public, they all had another thing in common: Each case was uncovered by an outside agency, not the Internal Affairs Bureau of the New York Police Department, the unit responsible for unearthing and investigating officers’ wrongdoing.

This spate of unrelated corruption prosecutions, and what some see as the Internal Affairs Bureau’s spotty record of uncovering major cases involving crooked officers, raise questions about the department’s ability to police itself, said nearly a dozen current and former prosecutors who have handled corruption cases, as well as some current and former Internal Affairs supervisors and investigators.

Several of them blamed a lack of effective outside oversight of the department’s anticorruption program, characterizing the monitoring as weak at best in recent years, with monitors having neither the political will to press the department nor support from City Hall. They also cited low starting salaries for new officers, poor morale, recruits drawn from a smaller pool of qualified candidates and a hidebound Internal Affairs Bureau bureaucracy.