A D.C. Superior Court jury took less than an hour yesterday to convict a 36-year-old District man of first-degree murder in the shooting death in January of D.C. police Sgt. Joseph M. Cournoyer at the Minnesota Avenue Metrobus terminal.

Jury members later described their decision to convict Sylvester R. King Jr., of 3697 Jay St. NE, as "cut and dry." King, who smiled slightly as the verdicts were read, said in a videotaped statement at the time of his arrest that his gun fired accidentally during a struggle with Cournoyer and that he was sorry "it happened."

Cournoyer's widow Darlene, sitting in the courtroom's second row with family members and friends, cried quietly as the jury foreman firmly answered "guilty" to all the charges brought against King.

Later, Darlene Cournoyer, who sat nearly expressionless throughout the five-day trial, smiled and thanked prosecutor Alan Strasser.

In addition to the charge of first-degree murder while armed, King was found guilty of six other charges stemming from the Jan. 29 slaying and the robbery minutes earlier of a Murry's Steaks store at 4061 Minnesota Ave. NE. Each charge, including armed robbery and assaulting a police officer with a dangerous weapon, carries a maximum life penalty.

Two other men, Charles A. Blackwell, 27, of 3693 Jay St. NE, and David A. Corbin, 20, of 3519 Jay St. NE, pleaded guilty earlier to second-degree murder charges in the robbery and killing.

At the time of his arrest, King was on parole on a burglary charge and had been convicted earlier of several felonies. He must be sentenced to a mandatory 20-year jail term because he was armed, and U.S. Attorney Joseph E. diGenova said King faces a maximum penalty of about 110 years. "He should spend the rest of his natural life in prison," diGenova said.

Cournoyer's colleagues also praised the jury's findings. "There is satisfaction that the man got convicted. He took a friend away from all of us," said Sgt. Dovid Goldfarb, who had known Cournoyer since they joined the police force in 1978.

Jurors said after the verdict that there had been little disagreement that King and two other men robbed the Murry's Steaks store and that King subsequently shot Cournoyer after the police officer later escorted King off a Metro bus.

Jurors said the only point of contention was whether the shooting was intentional or an accident as King, who did not take the stand, claimed in the videotaped statement. A witness testified that the morning after Cournoyer was killed, she heard King say that "it was either him or me" as he and a friend watched a television news account of the shooting.

Alice Stewart, a jury member who said she initially argued that King shot Cournoyer because he "was afraid," said she was persuaded later by other jurors that testimony proved King was at least four feet from Cournoyer when he shot the officer through the heart.

A police officer testified during the trial before Chief Judge H. Carl Moultrie I that gunpowder residue would have been found on Cournoyer's body near the gunshot wound if there had been a close struggle. No gunpowder residue was found, the officer testified.

"All counts were easy except the first- or second-degree murder . . . ," said juror Allen Goldberg. "You had seven people who were able to identify him. You had his hand print on the bus . . . . At one point King could have put the gun down or he could have shot him in the arm or the leg and still run away," Goldberg said. "But he shot him through the heart."