The suspect in a U.S. movie theater massacre is expected to be formally charged with murder and attempted murder during a court appearance on Monday.

Prosecutors say they may seek the death penalty for suspect James Holmes.

Authorities say Holmes went on a shooting rampage in Aurora, Colorado, killing 12 people and wounding 58 others.

The July 20 attack took place during the midnight screening of the new Batman film The Dark Knight Rises. Police say Holmes threw a tear gas bomb in the theater before opening fire on the audience.

During his first court appearance a week ago, the suspect appeared dazed and unemotional.

Holmes – a former Ph.D. student in neuroscience – has refused to talk to police.