Bradley Cooper (WENN.COM)

Oscar nominee Bradley Cooper is speeding up production on his new biopic about the U.S. military's deadliest sniper after he was murdered in Texas last week.

The Hangover star snapped up the rights to retired Navy SEAL Chris Kyle's book, American Sniper: The Autobiography of the Most Lethal Sniper in U.S. Military History, via his production company last year, but screenwriter Jason Hall is now racing to rework the movie adaptation to include the Iraq veteran's death.

Kyle, 38, and his pal Chad Littleworth were killed last Saturday after trying to help another soldier, Eddie Ray Routh, get through a crippling case of post-traumatic stress disorder by taking him to a shooting range outside Fort Worth as a form of treatment.

Routh is accused of turning his gun on both men before fleeing the range. He was arrested hours later and has since been charged with both murders.

Cooper reveals he and Hall were "about to dive into" the project when they learned of Kyle's tragic death.

In an interview with NPR.org, he says, "I was at Walter Reed Hospital (in Washington, D.C.) meeting with veterans who have post-traumatic stress disorder, among many other ailments, and then all of a sudden I heard this thing and I just couldn't believe it."

Cooper, who will star as Kyle and serve as producer on the movie, has yet to announce a director for the project but he's keen to get cameras rolling as soon as possible because of the current debate about the need for tighter gun laws in America.

The star explains, "His story, first of all, needs to be told. And it's also relevant on two fronts. One, gun control, and two, the needs to address this - the many soldiers that are coming back with post-traumatic stress disorder."

The actor is no stranger to mental health disorders - he has landed an Academy Award nomination for his portrayal of a bipolar sufferer struggling to get his life back on track in Silver Linings Playbook, which was inspired by director David O. Russell's son, Matthew, who battles the same condition.

Cooper has since become an advocate for mental health awareness and joined Russell in Washington, D.C. on Thursday for a meeting with U.S. Vice President Joe Biden to discuss the topic.