Police Officer Kenneth Boss once was part of a group of officers who fired 41 shots at an innocent man.

The shooting, which killed Amadou Diallo, prompted some New Yorkers to grow increasingly distrustful of the police. Citing the notoriety of the shooting, the police commissioner, Raymond Kelly, has kept Officer Boss on restricted duty, meaning he cannot carry a gun.

Officer Boss has never wavered in his belief that he is a competent officer. Since the misdeed eight years ago, he has been demanding a second chance at policing. Today, he plans to file a federal lawsuit seeking the return of his gun. The lawsuit will claim that Officer Boss has demonstrated his capacity for sound judgment during a recent combat tour in Iraq, according to a copy of the complaint.

Officer Boss is the last of the four police officers involved in the Diallo shooting still at the department.

“I’ve been swimming upstream,” Officer Boss said of his unflagging efforts get back on full duty. “I couldn’t in good conscience fade away into obscurity.”

During an interview in the office of his attorney yesterday, Officer Boss said he wants vindication in the eyes of his fellow officers and residents of the city, and he wants to be promoted to detective.

“The reason I’ve stayed is that I always believed I have had something to contribute in a positive way,” Officer Boss, 35, of Ronkonkoma, said.

Officer Boss was acquitted of murder in 2000, along with the three other officers, for the shooting. A departmental review cleared him of violating police rules.

Shortly thereafter, he found himself shouldering a very difficult duty. For nine months after September 11, 2001, he participated in cleaning up ground zero. This experience, coupled with a desire to prove his competence, he said, led him to enlist in the Marine Corps for a tour in Iraq.

After his seven-month tour in Iraq ended last October, Officer Boss said, “I believed that I had at least a compelling argument to get an audience with the police commissioner.”

His combat experience had earned him two letters from his commanding officers, testifying to his courage under fire and his ability to abide by the rules of engagement. In one letter, Officer Boss’s company commander, Captain Gary Koon, described how Officer Boss, after being knocked down when a bullet hit his body armor, managed to return “accurate fire” at one enemy fighter and capture a second.

In the second letter, which is addressed to Commissioner Kelly, another of Officer Boss’s commanders, Major Craig Abele, wrote: “I would be willing to stand before anyone and tell him why Officer Boss deserves to regain full-duty status.”

Officer Boss said that while the Diallo shooting was not uppermost in his thoughts in Iraq, “the lessons I learned from that night are with me.”

Those lessons appear to be with Officer Boss when he considers the restraint of his fellow Marines on the day he was shot. They declined to fire a machine gun in order to minimize the danger to Iraqi civilians, he said.

Officer Boss’s attorneys, Edward Hayes and Rae Koshetz, said nothing came of their request to have Commissioner Kelly reconsider Officer Boss’s status. The New York Police Department describes Officer Boss’s employment as “non-enforcement duty status.” Officer Boss describes his status as being “put out to pasture.”

Officer Boss continues to earn his $65,000-a-year salary at Floyd Bennett Field in Brooklyn, where he has no regular duties, he said. Many days he fixes power tools.

Fellow officers, Officer Boss said, have told him to be thankful.

“I hear repeatedly that at least, you’re collecting a paycheck,” Officer Boss said. “But there is no honor, no integrity, no reward in doing this work.”

As a police officer, Officer Boss last possessed a gun on February 4, 1999, the day of the shooting, he said. Today, his police identification cards are emblazoned the words “no firearm.” Fellow police officers have labeled him “Kenny-No Gun,” he said.

The lawsuit alleges that Officer Boss has been denied due process.

“He has been effectively terminated as a full-duty officer without any hearing,” Ms. Koshetz, who is a former police deputy commissioner for trials, said. “It’s wrong.”

Officer Boss sued the police department once before over his status. In that 2004 case, a state judge, Michael Stallman, found the police commissioner had the discretion to decide whether to reinstate an officer to full duty.

In an affidavit submitted then, Commissioner Kelly said the department would “be inappropriately subjected to pre-judgment” were Officer Boss to “take any police action involving the use of any force.”

If Officer Boss wins his lawsuit, he said he would like to join the bomb squad, because of his experience in locating roadside bombs in Iraq.

Should he lose his lawsuit, Officer Boss said he would remain at the department. “I can try to finish up my career.”