James Holmes was spared the death penalty and will serve life in prison without possibility for parole for killing 12 and injuring many more.
The jury consisting of nine women and three men could not reach a unanimous verdict on each of the murder counts.
Holmes murdered 12 people and left 70 others injured after he opened fire during a screening of The Dark Knight Rises at a cinema in Aurora, Colorado, on 20 July 2012.
Prosecutors said that the shooter deserved the death penalty because he had "meticulously" planned the attack, listening to loud techno while attacking victims to prevent himself from hearing them scream.
"I shot at people trying to get away. I shot at people trying to leave the theatre, to make sure others wouldn't follow," he reportedly told a psychiatrist.
The jury previously dismissed the idea that mental illness was a factor given the severity and grotesque nature of the massacre. More people would've died if it weren't for Holmes' weapon jamming, an AR-15 with 218 bullets unfired.
The formal sentencing hearing for Holmes will begin on August 24 and last three days, 9News Denver reported.
Additional reporting by the Associated Press.
