Colorado prosecutors charged James Holmes on Monday with 140 counts of murder or attempted murder, including 12 of first-degree murder for each fatality in the Aurora cinema shooting.
Holmes (24) was also slapped with one count of possession of an explosive device, and one sentence enhancement count.
Twelve people were killed and 58 were wounded after a gunman burst into a sold-out midnight viewing of the latest Batman film, The Dark Knight Rises, and began shooting people at random.
Holmes faces one count of first degree murder for each victim in addition to a second charge of "murder by depraved indifference." He also faces 116 attempted murder charges.
Prosecutors have said it will be several weeks before a decision is made on whether or not to seek the death penalty. Only one person has been executed in Colorado since capital punishment was reinstated in 1976.
Holmes gained access to the movie theatre via a fire exit shortly after the start of the highly-anticipated film's premier on 20 July and threw two canisters of noxious gas into the auditorium, witnesses and police said.
After firing into the air with a pump-action shotgun, the former graduate student allegedly began shooting people with a military-style assault rifle capable of firing 50 to 60 rounds a minute.
Ten victims from the theatre shooting remained hospitalised — four of them in critical condition.
Among them is Ashley Moser (25), whose six-year-old daughter Veronica was killed in the massacre. Moser was shot in the neck and stomach and has since lost her unborn child.
There has been speculation that stress over failing an important oral exam may have been the trigger that caused Holmes, a promising neuroscience student who had won a prestigious government grant, to become unhinged.
ABC News' affiliate in Denver, KMGH-TV, reported that Holmes purchased a high-powered rifle on 7 June, hours after failing the key oral test. Three days later, he dropped out of his university programme.