BOISE, Idaho -- An Idaho soldier has been released from prison four years after he admitted shooting an unarmed Afghan boy for sport and posing for photographs with the victim's corpse as part of what prosecutors described as a series of thrill killings by a rogue group of U.S. troops.

Andrew Holmes, 25, left Fort Leavenworth, Kansas, and flew home Sunday evening to the Boise Airport, where he was greeted by dozens of friends and relatives. His mother, Dana Holmes, told KTVB-TV that his relatives are "grateful to have him home and look forward to having this chapter of our lives closed."

Holmes was one of five soldiers from a Washington state-based Stryker brigade who were arrested in Afghanistan in 2010 in what prosecutors described as a conspiracy to kill civilians for fun. After the first killing, one of Holmes' fellow soldiers tried to blow the whistle on the plot, but the warnings went unheeded and the soldiers murdered two more civilians over the next few months.

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The killings, in Kandahar Province, were among the most serious war crime allegations of the Afghanistan war before another soldier from Washington state's Joint Base Lewis-McChord, Robert Bales, slaughtered 16 villagers in March 2012.

Holmes was accused of directly participating in the first killing, of a 15-year-old boy named Gul Mudin, and he was initially charged with conspiracy, premeditated murder and other charges before making a deal with prosecutors. He pleaded guilty in September 2011 to committing murder by an inherently dangerous act, possessing a finger bone from his victim and smoking hashish, and a judge sentenced him to seven years.

In court when he made the guilty plea, Holmes, then a private, acknowledged that he fired a heavy machine gun at a startled, unarmed civilian from 15 feet away after a co-defendant, then-Cpl. Jeremy Morlock, tossed a grenade at him. The man posed no threat, Holmes said.

"I looked at the young man. He was standing there like a deer in the headlights," he told the judge in a clear, steady voice. "I fired six to eight rounds at the man, and I've regretted it ever since."

At the time, Holmes' attorney, Daniel Conway, blamed his client's troubles on the unluckiness of having been assigned to such a dysfunctional unit. Holmes went into the Army as a good-natured teen who liked to play golf and go fishing, but would leave it as a felon, Conway said.

Morlock, of Wasilla, Alaska, was sentenced to 24 years in prison. The highest-ranking soldier charged, Staff Sgt. Calvin Gibbs, of Billings, Montana, was sentenced to life in prison with the possibility of parole after 10 years.