WASHINGTON >> A former State Department contractor sentenced to life in prison for his role in the 2007 shooting deaths of unarmed Iraqi civilians is asking for a new trial because of what he says is newly discovered evidence.

Lawyers for former Blackwater employee Nicholas Slatten said they received a State Department report two days before the Aug. 14 sentencing that they say casts doubt on prosecutors’ argument that Slatten is prone to unprovoked violence.

The document concerns a rescue mission of a downed aircraft that took place one week before the shooting in the case. Prosecutors invoked the earlier episode at Slatten’s trial, saying “this man either takes unprovoked shots where no threat is present, or he urges other people to do that.”

Slatten’s lawyers say the document, which they received from a third party, shows Army forces reported incoming fire from Iraqi insurgents before Slatten and other Blackwater contractors arrived at the site.

“It forcefully rebuts the government’s false narrative that Mr. Slatten shot his weapon at a building when no threats were present and provoked his teammates and the Army to do the same,” Slatten’s lawyers wrote in arguing for a new trial. “The government’s failure to disclose the document and any other similar information, and its presentation of a misleading narrative at trial, require a new trial.”

Defense lawyers say Slatten’s sister received the document in an email from someone who worked for Blackwater in Baghdad in September 2007. The lawyers say they have no record of prosecutors having previously produced the document.

Slatten was convicted of first-degree murder last December in connection with a September 2007 massacre at a crowded Baghdad traffic circle. Prosecutors alleged that an unprovoked Slatten was the first to fire shots, killing 19-year-old Ahmed Haithem Ahmed Al Rubia’y, who was driving his mother to an appointment.

Slatten has said he was a victim of an “unjust prosecution” and that government lawyers cared more about producing a conviction than uncovering the truth of what happened in Baghdad 12 years ago.

At his sentencing hearing, he called the proceedings a “miscarriage of justice” that “will not stand.”

Three other Blackwater contractors — Paul Alvin Slough, Evan Liberty and Dustin Heard — were found guilty at trial of charges including voluntary manslaughter and attempted manslaughter .

A spokeswoman for the U.S. attorney’s office in Washington declined to comment today.