LOS ANGELES -- The family of a U.S. soldier killed in Afghanistan sued a Canadian military contractor for rehiring a security guard, an Afghan national, after he allegedly threatened to attack U.S. troops and eventually ended up killing two service members and wounding four others.

The federal wrongful death lawsuit filed Monday claims Tundra Strategies failed to document threats made by Shir Ahmed and didn't report to U.S. military officials the danger he posed before the March 2011 attack at Forward Operating Base Frontenac.

The shooting was a factor in the screening improvements of Afghan nationals hired to provide security for U.S. and coalition forces.

Among those killed was medic Rudy Acosta, 19, of Santa Clarita, California, whose family along with three other survivors, are named plaintiffs in the lawsuit.

A phone message left for Tundra was not immediately returned Tuesday

The lawsuit said Tundra, hired in November 2009 by the U.S. government to screen and monitor private security guards at nine military installations, did not adhere to its basic duties in dealing with Ahmed, who was hired by the company in May 2010.

Ahmed was fired two months later after he was accused of threatening to kill U.S. and coalition troops, according to the lawsuit. Despite a Tundra manager's concern that Ahmed not be hired again, the Ontario-based firm brought Ahmed back in early 2011.

The lawsuit said the shooting was avoidable and Tundra management did not record Ahmed's threats or flag that he was a potential danger to re-hire.

U.S. military officials later said Tundra records showed Ahmed wasn't deemed a threat because the allegations against him were unsubstantiated.

"All we know at this point is (Tundra) didn't do what it was hired to do," said plaintiffs' attorney Michael Doyle. "It was clear enough that this guy shouldn't be given a weapon around the troops."

Within days of being hired again, Ahmed opened fire on U.S. troops as they were cleaning their weapons for an upcoming mission. Ahmed, who was wearing body armour, unloaded the first magazine of his Tundra-issued AK-47 before reloading, according to the lawsuit.

Other U.S. troops returned fire and eventually killed Ahmed.

Security companies that hire Afghans are required to vet an applicant by checking their identities, work history, and other personal information, as well as police checks, fingerprinting and other biometric information such as iris scans and photographs.

The contractors also have to report individuals who turn out to be security risks.

U.S. military officials have since beefed up the process by having random checks of private security companies but have warned the added safeguards won't eliminate the problem.

Doyle said the lawsuit was filed to hold military contractors accountable for their role during wartime.

"If there aren't any consequences, it's a continuing danger to the troops and that's not acceptable," he said.