The jury was tasked with deciding whether Holmes knew the nature of his crime or could distinguish between right and wrong at the time he committed the act. There was also the Irresistible Impulse Test: whether, even if Holmes could tell right from wrong, he was under such duress from mental disease that he had lost the free will to choose between the two.
The Verdict: Guilty
The burden was on prosecutors to prove Holmes' sanity and the jury heard competing testimony from doctors who evaluated his mental state. In the end, the jury determined Holmes could understand the nature of his actions and that he was in control of his actions.
While the jury's completed verdict form hasn't been released yet, you can read the instruction form the jury received from the court. The documents reveals a sense of the scope of the charges and the difficulty of the jury's task.