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.
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.
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.
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.