On the afternoon of July 8, 2006, four private security guards rolled out of Baghdad's Green Zone in an armored SUV. The team leader, Jacob C. Washbourne, rode in the front passenger seat. He seemed in a good mood. His vacation started the next day.

"I want to kill somebody today," Washbourne said, according to the three other men in the vehicle, who later recalled it as an offhand remark. Before the day was over, however, the guards had been involved in three shooting incidents. In one, Washbourne allegedly fired into the windshield of a taxi for amusement, according to interviews and statements from the three other guards.

Washbourne, a 29-year-old former Marine, denied the allegations. "They're all unfounded, unbased, and they simply did not happen," he said during an interview near his home in Broken Arrow, Okla.

The full story of what happened on Baghdad's airport road that day may never be known. But a Washington Post investigation of the incidents provides a rare look inside the world of private security contractors, the hired guns who fight a parallel and largely hidden war in Iraq. The contractors face the same dangers as the military, but many come to the war for big money, and they operate outside most of the laws that govern American forces.

The U.S. military has brought charges against dozens of soldiers and Marines in Iraq, including 64 servicemen linked to murders. Not a single case has been brought against a security contractor, and confusion is widespread among contractors and the military over what laws, if any, apply to their conduct. The Pentagon estimates that at least 20,000 security contractors work in Iraq, the size of an additional division.

Private contractors were granted immunity from the Iraqi legal process in 2004 by L. Paul Bremer, head of the Coalition Provisional Authority, the U.S. occupation government. More recently, the military and Congress have moved to establish guidelines for prosecuting contractors under U.S. law or the Uniform Code of Military Justice, but so far the issue remains unresolved.

The only known inquiry into the July 8 incidents was conducted by Triple Canopy, a 3 1/2 -year-old company founded by retired Special Forces officers and based in Herndon. Triple Canopy employed the four guards. After the one-week probe, the company concluded that three questionable shooting incidents had occurred that day and fired Washbourne and two other employees, Shane B. Schmidt and Charles L. Sheppard III.

Lee A. Van Arsdale, Triple Canopy's chief executive officer, said the three men failed to report the shootings immediately, a violation of company policy and local Defense Department requirements for reporting incidents. He said Triple Canopy was unable to determine the circumstances behind the shootings, especially since no deaths or injuries were recorded by U.S. or Iraqi authorities.

"You have to assume that, if someone engages, he is following the rules and that he did feel a threat," Van Arsdale said, adding that conflicting accounts, delays in reporting the incidents and lack of evidence made it impossible to determine exactly what provoked the shootings. Triple Canopy officials said they have lobbied for more regulation of contractors since 2004 to better define how incidents such as the July 8 shootings are reported and investigated.

Many details about the shootings are in dispute. This account is based on company after-action reports and other documents, court filings, and interviews with current and former Triple Canopy employees, including all four men riding in the armored Chevrolet Suburban that day.

Schmidt and Sheppard said they were horrified by what they described as a shooting rampage by Washbourne and waited two days to come forward because they feared for their jobs and their lives. The two have sued Triple Canopy in Fairfax County Circuit Court, arguing that the company fired them for reporting a crime.

But another man in the vehicle, Fijian army veteran Isireli Naucukidi, said Sheppard, who was driving, cut off the taxi on Washbourne's orders, giving him a better shot. Naucukidi said the three American guards laughed as they sped away, the fate of the Iraqi taxi driver unknown. Schmidt told Washbourne, "Nice shot," according to Naucukidi.