The man identified as the lookout in last year's deadly robbery of Colonel Brooks' Tavern pleaded guilty yesterday in D.C. Superior Court to three counts of second-degree murder, in what appeared to be a deal to cooperate against his two surviving co-defendants.

Standing next to his attorney, Thomas Heslep, in a nearly empty courtroom, Joel A. Smith, 22, admitted his role in the robbery that left three employees dead at the Northeast Washington restaurant.

A popular Sunday brunch spot not far from Catholic University, Colonel Brooks' has been a fixture in the Brookland neighborhood for about a quarter of a century. The execution-style slayings, carried out inside the restaurant's walk-in freezer, stunned residents throughout the city.

For months, the case remained open. But a number of breakthroughs culminated in January in the arrests of three suspects and the death of the suspected ringleader, who killed himself as police were closing in on him outside Richmond.

Exactly what Smith's plea agreement entails was unclear yesterday because the judge, Robert I. Richter, did not enter it into the court file and refused to release it.

Such plea agreements usually require the defendant to cooperate in the prosecution of any co-defendants. In instances where news of a plea could compromise the prosecution's case, judges can seal the terms of the agreement. No such motion to seal was made in this case, however.

When asked yesterday whether Smith is cooperating in the prosecution of the other two defendants, Tyree S. Bunn, 27, and Rodman J. Durham, 29, the lawyers in the case declined to comment.

From the outset, investigators suspected that the botched robbery had been conceived by a current or former employee, who would have known that the previous night's receipts would still be on hand and that the early morning setup staff was an easy mark.

But the initial suspect -- a manager who hid during the robbery -- was not involved, and it was months before investigators identified ex-employee David A. Wright as the man they believed had planned the April 6, 2003, robbery.

Wright, 33, had been fired from his job as a cook at Colonel Brooks' the previous summer, but he had been there long enough to know the restaurant's vulnerabilities. He enlisted two friends and his cousin, Smith, in plans to rob the tavern, in the 900 block of Monroe Street NE, prosecutors said in court papers filed yesterday.

But the robbery, which unfolded just after 8 that Sunday morning, went awry. One of the employees, Neomi Payne, 48, recognized Wright, who hadn't fitted his mask properly, and Wright decided he could not afford to leave any witnesses, prosecutors said.

"They got to go," he told his accomplices, according to the account of the killings outlined yesterday by Assistant U.S. Attorney Ronald W. Sharpe.

Wright and Durham then entered the freezer, and amid the shrieks and screams of the three victims, shot Payne and her co-workers, Rodney Barnes, 47, and Joshua Greenberg, 34, Sharpe said. He said the four men then fled with about $3,000, which they divided among themselves at Smith's apartment on Kendall Street NE.

It wasn't until that July that investigators, led by D.C. police Detective Mitch Credle, turned up the first links to the eventual suspects. Someone told investigators that Bunn had been bragging about the killings. By December, investigators had persuaded this witness to conduct a secretly videotaped conversation with Bunn, in which he again described the killings and his role in them. By the end of January, Bunn, Durham and Smith were in custody.

A grand jury indicted the three men this week. Each was charged with multiple counts of first-degree murder, each of which carries a 30-year minimum prison term.

James Williams, the attorney for Bunn, said he was not surprised that Smith had pleaded guilty. "But it's too early to tell if it's going to change Mr. Bunn's thinking about whether he wants a trial," Williams said.

Fred Sullivan, Durham's attorney, did not return a phone call seeking comment.

By pleading to second-degree murder, Smith faces a minimum of only five years in prison on each of the three counts. The maximum on each is 40 years.

Rudy Manili, the general manager of Colonel Brooks', said he could live with the plea by Smith, particularly if it brings the rest of the case to a resolution. "If the government determined that it was going to have one of them plea, so they could be a witness for the prosecution, it should have been the one that had the least to do with the murders, and from everything I've been told, Joel was that person," Manili said.

Joel A. Smith pleaded guilty to three counts of second-degree murder.

Colonel Brooks' Tavern employees Joshua Greenberg, 34, left, Neomi Payne, 48, and Rodney Barnes, 47, were killed during a robbery as they prepared the tavern for Sunday morning brunch on April 6, 2003. Prosecutors say Payne had recognized one of the robbers.