(CNN) -- Twelve people walked into a Colorado movie theater late one July night, expecting to enjoy a special midnight screening of the Batman film, "The Dark Knight Rises."
They didn't walk out.
Their deaths -- and injuries to dozens of others -- came after a man dressed head to toe in protective tactical gear sprayed the Century 16 theater in Aurora with bullets from an AR-15 rifle, a 12-gauge shotgun and a .40-caliber pistol, weapons police discovered at the scene.
On Monday, many grisly details of what happened could be presented in a Colorado court at a preliminary hearing for the shooting suspect, James Holmes.
Now 25, Holmes faces 166 charges, including murder, attempted murder and weapons offenses, tied to the July 20 rampage.
Bits and pieces emerged from police and witnesses shortly after the massacre. One was that Holmes had colored his hair red and told police he was "the Joker," one of Batman's archenemies, according to a federal law enforcement source with detailed knowledge of the investigation.
But much information has been kept under wraps, especially after Arapahoe County District Judge William Sylvester issued a gag order to prevent defense lawyers, prosecutors and law enforcement agencies from disclosing certain information to the media.
That could change after this week's hearing, which is expected to last several days.
Prosecutors are expected to call scores of witnesses and outline their evidence in the case. Holmes's attorneys, meanwhile, are expected to argue he has "diminished capacity," a term that, according to the Colorado Bar Association, relates to a person's ability or inability "to make adequately considered decisions" regarding his or her legal representation because of "mental impairment or for some other reason."
After the hearing concludes, Sylvester will determine whether there is enough evidence for Holmes to stand trial.
While officials and news reports have shed light on Holmes, his motive hasn't been spelled out.
He was a doctoral student in the neuroscience program at the Anschutz Medical Campus of the University of Colorado, Denver, in Aurora, until he withdrew a month before being arrested outside the bullet-riddled movie theater. Holmes had been a patient of a University of Colorado psychiatrist, according to a court document filed by his lawyers.
Authorities later discovered that his sparsely decorated Aurora apartment was booby-trapped with more than 30 homemade grenades and 10 gallons of gasoline, a law enforcement official who saw video showing its interior told CNN. Authorities intentionally detonated two rigged explosives in order to access the third-floor, one-bedroom apartment.
What spurred him to rig his apartment in such a way and to later fatally shoot strangers is not clear. Academically, Holmes excelled at the University of California, Riverside, according to Chancellor Timothy P. White.
His only brush with the law in Colorado appears to have been a 2011 summons for speeding from Aurora police.
The horror Holmes allegedly unleashed inside the movie theater has been better documented, thanks to accounts from survivors and law enforcement sources.
After the movie started, the suspect went out a rear exit door, propped it open, gathered weapons, then re-entered through the same door, according to a source. He then tossed in a canister before starting to shoot.
Screaming moviegoers scrambled to escape from the gunman, who shot at random as he walked up the theater's steps, witnesses said.
It was a scene "straight out of a horror film," said Chris Ramos, who was inside the theater.
"He was just literally shooting everyone, like hunting season," Ramos said.
Holmes surrendered without resistance within seven minutes of the first calls from panicked moviegoers reporting the shooting, Aurora Police Chief Dan Oates said.
Meanwhile, local hospitals found themselves overwhelmed with victims, including one who was just 4 months old. Soon thereafter, 12 families heard the horrifying news that their loved ones were dead.
"This is an act of evil," Colorado Gov. John Hickenlooper told CNN.