Photographs of four of the five officers involved in the fatal shooting of Sean Bell have been released just as a Queens grand jury is set to hear evidence in the case, attorneys involved in the proceedings said yesterday.

The photographs of Detectives Paul Headley, Marc Cooper, Michael Oliver and Officer Michael Carey were released by the police department over the weekend in response to a Freedom of Information request filed by The New York Sun. A photograph of the fifth officer involved in the shooting was not released because he works undercover. That officer, Detective Gescard Isnora, reportedly shot the first of 50 bullets fired at Bell and two others outside the Kalua Cabaret in Jamaica on November 25.

Attorneys involved in the case said a grand jury could begin hearing evidence as early as today.

“It is happening,” an attorney who represents the Bell family, Neville Mitchell, said. “We are aware that they are starting to hear the case on Monday,” Mr. Mitchell, who met with representatives of the Queens district attorney last week, said.

A spokeswoman for District Attorney Richard Brown declined to comment on when the grand jury would be convened. “The grand jury secrecy requires that we not comment,” the spokeswoman, Nicole Navas, said. She said the district attorney promised a thorough, fair, and impartial investigation.

An attorney who represents several witnesses to the shootings, Charlie King, confirmed that his clients would testify in the near future. “I expect my witnesses will be called toward the end of the week, or early next week,” Mr. King said.

It is unclear which officers involved in the shooting will testify. An attorney representing Mr. Cooper, Paul Martin, said the 17-year veteran officer would testify. “I believe my client’s actions, as they relate to the shooting, were reasonable under the circumstances,” Mr. Martin said. He said his client fired once.

An attorney for Mr. Carey, Stephen Worth, said he and his client were undecided about testifying. Attorneys representing messrs. Isnora, Headley, and Oliver — the latter of whom allegedly fired 31 times — could not be reached for comment yesterday.

Observers said the grand jury proceedings could take several weeks, or months. As a charging body, the 23 individuals who make up the grand jury will hear evidence and deliberate during closed-door proceedings. They may hand down an indictment if a majority of the group votes to do so.

Key developments expected to emerge from the proceedings include whether the officers who testify will waive their rights to immunity, a professor at Pace University’s School of Law, Bennett Gershman, said. If they do so, it may indicate they are not targets of the prosecutors’ evidence, Mr. Gershman, who served on the Grand Jury Project in 1997, said.

“It’s possible that the prosecutors have come to a conclusion that some officers were on the periphery of this incident and these are the kinds of witnesses that the prosecutor would want to testify without their fear of beings indicted,” Mr. Gershman said.