It took no more than a heartbeat for the courtroom to explode around Larry C. Hackett yesterday. The only D.C. police officer ever tried for first-degree murder, his acquittal in D.C. Superior Court unleashed 19 months of pent-up rage.

As forewoman Angela K. Halladay, trembling slightly in the jury box, called out the third "not guilty" verdict -- to first-degree murder, then second-degree murder, then manslaughter -- Hackett looked down briefly and let out a breath. His wife, lips quivering, embraced two companions in the third row of spectators.

Two close friends of the slain man, Sylvia Edon and Camille Anderson, wailed and stormed outside. Grady McCray, the widow of Stanley McCray, laid her head in her hand and then stopped moving.

"You will never have peace, Hackett!" Edon screamed when the acquitted man emerged moments later. "You gonna get yours! You didn't get it in the court, but you gonna get it!"

Hackett, walking briskly and silently, left the courthouse without a reply. He did not return a call to his home, and his wife declined to talk about the case.

The 36-year-old lieutenant, the highest-ranking D.C. police officer ever tried here for any crime, was off duty when he shot McCray outside Lefty's Cocktail Lounge in Northeast Washington about midnight on March 4, 1989.

Jurors in the nine-day trial heard two principal versions of the struggle. The government called it premeditated murder. Hackett said he fired in self-defense.

In the account laid out by Assistant U.S. Attorney William J. Hochul Jr., Hackett was asked to leave the bar after drinking and growing abusive. Witnesses for the prosecution said he tried after his departure to prevent other patrons from entering and soon got into a fistfight with McCray.

The witnesses, including a D.C. police officer and another officer from the U.S. Capitol Police, said Hackett pulled his service revolver after bystanders broke up the fight. "What are you going to do? Shoot me?" McCray is said to have asked. Hackett, the witnesses said, then did so.

Hackett, who took the stand in his own defense, put forth an altogether different sequence of events. He said McCray and a friend attacked and beat him savagely. Someone, he testified, called out, "He's got a gun!" Hackett reached for his service revolver, he said, and shot once at a figure rushing toward him.

McCray, who died of a chest wound, was unarmed.

Measured and articulate, Hackett aimed his gaze and his testimony directly at the jurors in the box. "Ladies and gentlemen, unless you laid on the ground while somebody beat you to submission, I might not be able to tell you."

In assessing the two accounts, jurors said yesterday they gave great weight to two items of physical evidence: a life-size cardboard silhouette of the dead man, and the overcoat he was wearing when he died.

The silhouette, four jurors said, depicted McCray -- as government witnesses described him -- standing erect and still at the moment the shot was fired. Yet the overcoat, they said in interviews, had no hole in its back corresponding to the dead man's exit wound from a .38 caliber slug. The jurors said they concluded that McCray was lunging, his coattails swinging, when he died.

"Some people thought 70 percent that he murdered the guy and only 30 percent that it was self-defense," said Halladay, the forewoman. "We all have to live with doubt."

Hackett was tactical operations commander of the 4th District.

The department moved swiftly to arrest him after the shooting, with Capt. William Ritchie, of the homicide squad, and then-deputy chief Isaac Fulwood Jr. traveling to the scene.

But the family and friends of the dead man said they always doubted that a high-ranking officer would be convicted.

"He's walking because he's a lieutenant, and justice sticks up for the lieutenants," Grady McCray said after the verdict yesterday.

Following standard practice, the department suspended Hackett without pay when he was formally charged. It would be standard practice now to restore his pay and place him in a job that involves no contact with the public, pending an administrative review.

"What he did may not have risen to criminal conduct in the eyes of the jury, but that doesn't mean it didn't rise to a serious administrative infraction," said Gary Hankins, labor committee chairman of the Fraternal Order of Police, who predicted that Hackett would be brought before a police trial board. "It can cost you your job."

Police officials and spokesmen did not return telephone calls yesterday.