BOULDER, Colo. -- A man accused of shooting at a Longmont police officer who was trying to arrest him says he thought he was being chased by a zombie.

Brandon Michael Duke, 22, faces charges of first-degree attempted murder, first degree assault, felony menacing, possession of a weapon by a previous offender, all felonies, and misdemeanor carrying a concealed weapon, resisting arrest, obstructing a police officer, and reckless endangerment, according to court records.

Duke pleaded not guilty by reason of insanity on Friday in court.

Authorities said Longmont officer David Blake chased Duke along Main Street on May 8, and was trying to arrest him on an outstanding warrant when the confrontation took place.

Duke told investigators he thought the officer was a zombie and he only shot at him as a warning because he was trying to protect himself. The officer returned fire, striking Duke in the torso and arm. A bullet also grazed his forehead.

Duke will undergo a mental health evaluation and the report will be reviewed in court on Dec. 3.