A D.C. man who police said was the lookout in a Northeast Washington robbery that led to the slaying of a D.C. police sergeant was sentenced yesterday to at least 16 years in prison.

David A. Corbin, 20, of 3519 Jay St. NE, who had pleaded guilty to second-degree murder and armed robbery, was the third and last man to be sentenced in the Jan. 29 death of Sgt. Joseph M. Cournoyer.

Cournoyer, a six-year member of the force, was shot after he escorted another defendant, Sylvester R. King Jr., off a crowded bus for questioning about the robbery of a nearby meat store. King, convicted of shooting Cournoyer, was sentenced Tuesday to 79 years to life.

Assistant U.S. Attorney Alan Strasser asked D.C. Superior Court Chief Judge H. Carl Moultrie I yesterday to consider that Corbin identified King as the man who had shot Cournoyer, which helped police to make a quick arrest. Still, Strasser said, Corbin was involved in a robbery that resulted in a death.

Corbin said that he was sorry and well aware of the seriousness of his offense. "The nature of such an offense will never change," he said, but the nature of a human being can.

Moultrie noted Corbin's level of involvement and his help given to the police.

"But there was a death in this case . . . ," Moultrie said, sentencing Corbin to 16 to 48 years in prison.