Attorneys for James Holmes open their case Thursday, and they plan to offer a less emotional, more clinical assessment of the Colorado theater shooter after two months of often-gruesome testimony from prosecution witnesses.

Without the scores of victims on their side, Holmes' defense team plans to present its evidence in less than a quarter of the time taken by prosecutors.

The attorneys have said their case will focus tightly on mental illness in a bid to prove to jurors that Holmes was legally insane when he opened fire on a packed movie premiere in 2012, killing 12 people.

Even if Holmes' team is unsuccessful, legal experts say, the coming days may be the attorneys best chance to convince jurors that he should not be executed if he is convicted.