Colorado grocery store gunman charged with another 43 counts of attempted murder, weapons and assault charges

Alissa was initially facing 10 counts of first-degree murder

Colorado prosecutors have charged the man who fatally shot 10 people at a Boulder grocery store on March 22 with an additional 44 counts of attempted murder, weapons and assault charges.

Ahmad Al Aliwi Alissa, 21, was initially facing 10 counts of first-degree murder and one count of attempted first-degree murder when he was apprehended on March 23; he now faces 54 total charges.

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The additional charges include 32 additional counts of attempted first-degree murder, 10 counts of unlawful use of a high-capacity magazine and one count of first-degree assault, according to a motion filed Wendesday in Boulder County District Court.

Ahmad Al Aliwi Alissa appears before Boulder District Court Judge Thomas Mulvahill at the Boulder County Justice Center in Boulder, Colo. (Helen H. Richardson/The Denver Post via AP, Pool, File)

Ahmad Al Aliwi Alissa appears before Boulder District Court Judge Thomas Mulvahill at the Boulder County Justice Center in Boulder, Colo. (Helen H. Richardson/The Denver Post via AP, Pool, File)

Alissa had bought a Ruger AR-556 pistol, which resembles an AR-15 rifle, six days before killing the 10 victims, including Boulder Police Officer Eric Talley. He passed a background check conducted by the Colorado Bureau of Investigation.

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He also had a 9mm handgun, but police do not believe he used it in the shooting and it's unclear how he acquired it. 

The motive behind Alissa's attack remains unclear. 

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The 21-year-old was previously known to the FBI when the bureau linked him to another individual under investigation, The New York Times reported in March.

Victims of the deadly shooting include Denny Stong, 20; Neven Stanisic, 23; Rikki Olds, 25; Tralona Bartkowiak, 49; Suzanne Fountain, 59; Teri Leiker, 51; Boulder Police Officer Eric Talley, 51; Kevin Mahoney, 61; Lynn Murray, 62, and Jody Waters, 65.

Fox News' Stephen Sorace and Paul Best contributed to this report.