A member of a rogue US Army unit has been sentenced to three years' prison after pleading guilty to killing an unarmed Afghan civilian in US custody in May 2010. Specialist Adam Winfield, 23, of Coral Gables, Fla., had been charged with premeditated murder, aggravated assault and conspiracy to commit murder in several incidents, including the deaths of three Afghan civilians in Kandahar Province. He pleaded guilty to the reduced charge of involuntary manslaughter in military court, along with one count of illegal use of marijuana, in exchange for his testimony against other soldiers accused in the killings. On Friday, his rank was reduced to private and Winfield was stripped of pay and allowances, as well as discharged for bad conduct. The Coral Gables, Florida man will get credit for the approximately 507 days he has already served in prison. Winfield's defense attorney, Eric Montalvo, said he felt the sentence was fair. "The government finally recognized that Adam Winfield was not a monster like Staff Sergeant Gibbs," Montalvo said. Winfield, who tried to blow the whistle on the murder plot, is among five soldiers accused of killing the civilians for sport and then planting evidence on the bodies to make it seem as though the victims had attacked the soldiers first. He is a member of the 2nd Battalion, 1st Infantry Regiment, 2nd Brigade, also known as the Stryker Brigade, based at Joint Base Lewis-McChord near Seattle. Another soldier in the unit, Private Jeremy Morlock of Wasilla, Alaska, was sentenced in March to 24 years in prison. Seven other service members have been charged with covering up the killings. Montalvo said the killings and widespread hash use in the field showed the unit lacked leadership. Under questioning by the judge, Colonel David Conn, Winfield admitted he had been aware he was committing a crime and that he failed to prevent it. "I had means to prevent this from happening, sir. I had a number of options to choose from that day, sir, to take the action necessary," Winfield said. "I failed because I was afraid, sir." He explained he feared retribution from his superior, Staff Sergeant Calvin Gibbs, the alleged ringleader of the rogue group of soldiers. Gibbs threatened to kill Winfield if he ever told anyone of the killings, Winfield said. Morlock testified that Gibbs suggested Winfield could not be trusted to keep quiet about the killings, and that he was a "liability" that needed to be removed. "He talked to me a couple times about the idea to take Winfield out, take him down to the gym and drop a weight on him," or stage another kind of accident, Winfield's platoon mate added. During a patrol on May 2, 2010, Gibbs pulled an Afghan civilian from his compound. Gibbs asked Winfield and Morlock: "Is this the one?" The implication was clear that the soldiers would kill the civilian, Winfield said. Gibbs threw a grenade at the man, and then Winfield and Morlock fired their weapons at him. Morlock later planted an unexploded grenade near the body. The platoon commander, Lieutenant Stefan Moye, was in a nearby compound and arrived on the scene when he heard the shots and explosions. Moye testified that he was told the dead man had thrown the grenade at the soldiers first, and that he never had a reason to doubt that story. A court martial for Gibbs is expected this fall. The three killings, including the incident to which Winfield pleaded guilty, took place near Forward Operating Base Ramrod in Kandahar Province, Afghanistan, where the Stryker Brigade was stationed. The murders were considered the worst abuses by active-duty military personnel since the Abu Ghraib scandal in Iraq, and a significant setback in the US attempt to win over the civilian population of Afghanistan in the war against the Taliban, Al-Qaeda and other insurgents.