James Holmes, the man suspected of shooting the victims at a cinema in Aurora, Colorado, is currently in police custody.
Veronica Moser-Sullivan (6), Jessica Ghawi (24), John Larimer (27), Alexander Boik (18), Jesse Childress (29), Jonathan Blunk (26), Rebecca Wingo (32), Alex Sullivan (27), Gordon Cowden (51), Micayla Medek (23) and Alexander Teves (24) all died on Friday (July 20).
The 12th victim has provisionally been identified as Matthew McQuinn, 27.
All the deaths were caused by gunshot wounds, a coroner has found. 58 people were injured in the massacre.
US President Barack Obama, Warner Bros and Dark Knight Rises cast member Gary Oldman among others have paid their respect to the dead and injured.
Officers are now preparing to enter Holmes's Aurora apartment, which is booby-trapped with explosives.