Accused "Batman" theatre gunman James Holmes was sane when he cold-bloodedly opened fire on a packed Colorado cinema three years ago, prosecutors said in closing arguments.
But the troubled 27-year-old's defence team insisted he should be found not guilty due to insanity over the July 2012 shootings, which killed 12 theatre-goers and injured 70 others in Aurora just outside Denver.
Wrapping up the two-and-a-half month trial, prosecutor George Brauchler ran through a blow-by-blow account of the massacre, which stunned the United States and reignited the country's perennial debate about gun control.
Referring to the 400 people in the theatre, he said: "They came in hoping to see a story of a hero dressed in black, someone who would fight insurmountable odds in the name of justice and trying to protect others.
"Instead a different figure appeared by the screen dressed all in black. And he came there with one thing in his heart and in his mind - and that was mass murder," the prosecutor said.
Holmes has been in custody since he was arrested outside the crowded midnight screening of The Dark Knight Rises on July 20, 2012.
He faces two counts of murder or attempted murder for each of the 82 victims.
Defence lawyer Daniel King said: "The fact of the matter is that when Mr Holmes stepped into that theatre... he had lost touch with reality.
"You cannot divorce the mental illness from this case, or from Mr Holmes," he said.
"The mental illness caused this to happen. Only the mental illness caused this to happen, and nothing else."
But Brauchler urged the court to "reject this claim that he didn't know right from wrong... That guy was sane beyond a reasonable doubt, and he needs to be held accountable for what he did".
Simply having a mental illness does not make a defendant insane under Colorado law, Brauchler said.
What matters, he said is "if he knows what society thinks is right or wrong".
Defence lawyers did not contest what happened in the massacre where Holmes lobbed smoke bomb-type devices into the theatre and randomly fired weapons including an AR-15 military-style rifle, a 12-gauge shotgun and a .40 calibre pistol.
His apartment was later found to be booby-trapped with an array of homemade explosive devices, which police had to disarm before entering the dwelling.
If he is found not guilty by reason of insanity, Holmes will be confined to a state mental hospital.
To win a release, he would have to be found free of mental illness and no longer a danger to himself or to others.