Three years ago, at a party thrown by U.S. civilian contractors in Iraq, a young ex-Marine named Jason Pope was shot to death by a drunken co-worker. Now, his family has filed a lawsuit in federal court claiming the military contractor, DynCorp International, and 12 of its employees conspired to cover up exactly how Pope died.

At first, news media in Detroit - Pope's home town - reported that he was killed while protecting U.S. diplomats in Iraq. But investigations by the State and Justice Departments found that, during a party at a U.S. embassy office in Erbil, Iraq, Pope and a fellow contractor, 27 year old Kyle Palmer, were horsing around with Pope's 9 millimeter Glock-19 handgun.

Federal prosecutors say, at various times, the two were actually pointing the gun at each other. Then Palmer, who was "considerably intoxicated," according to the Justice Department, fired the gun without checking whether it was loaded. The bullet struck and killed Pope, then 25 years old.

Both men had been working as security specialists, assigned to protect diplomats, dignitaries and civilian workers in Iraq. Pope joined the company after serving two tours in Iraq and Afghanistan.

In 2010, after a plea deal with prosecutors, a federal judge in Mississippi sentenced Palmer to 36 months in prison for involuntary manslaughter and ordered him to pay $6,000 in restitution and fines. But the lawsuit filed by Pope's family accuses DynCorp International and its employees of concocting a different story, falsely suggesting that Pope was drunk and shot himself.

The family's attorney, William Goodman, tells ABC News, "the autopsy showed that Justin had not a drop of alcohol or any other intoxicant in him."

What motive would DynCorp or its employees have for a cover-up? According to Goodman, the episode was deeply embarrassing to the company - one of only three major U.S. contractors operating in Iraq at the time. "They didn't want the American public to know its money was being spent on criminal and lethal behavior," Goodman said.

DynCorp International, based in Falls Church, Va., told ABC News in a statement: "This was an extremely tragic accident that occurred several years ago, after working hours, when certain personnel were drinking alcohol in violation of Company policy. Although our thoughts and prayers go out to Mr. Pope's family and loved ones, the allegations contained within the suit are without merit."