Jury selection is often the most interesting and challenging part of a trial for the attorneys involved and can also contribute to making or breaking a verdict. People come into the court with their predispositions and a lawyer's job is to weed out potential jurors who cannot put aside their predispositions for the sake of fairness and adherence to the law.

It can be a real challenge getting potential jurors to admit their biases, in particular because jurors often hide their real opinions in a deliberate attempt to either get on, or stay off, a jury.

Such inherent difficulties are multiplied one thousand-fold when it comes to a trial like the one involving James Holmes. He is accused of sneaking into a movie theater in Aurora, Colo., and opening fire on 421 people who were watching a midnight showing of the Batman movie "The Dark Knight Rises." Holmes ultimately killed 12 people, and 70 were injured.

Jury selection in his case started this week, and it was expected that no less than 9,000 potential jurors will be considered in a selection process that will no doubt take months to complete.

And it should take that long given the complexity of this super high-profile case.

Holmes has entered an insanity plea, so the jury members will need to be open and willing to consider it. Complicating the matter is the fact that Colorado boasts two legal definitions of insanity, and if Holmes meets only one of the two he will be sent to a mental health facility rather than to jail.

Under Colorado law, Holmes will be declared legally "insane" and therefore unfit to stand trial if he is (1) "so diseased or defective in mind at the time of the crime that he can not tell right from wrong" or (2) "has a mental disease or defect that prevents him from forming a culpable state of mind" [See CRS sec 16-8-101.5 and 103].

These types of issues are notoriously difficult for juries to consider on their face, but many potential jurors are reluctant to even consider an insanity defense in the first place.

Colorado makes it even more confusing because it is one of the few states where the prosecution is burdened with proving that a defendant is legally "sane" and therefore fit to stand trial [See Mundy v People, 105 Colorado 548, 1940].

This is an enormous burden but an even greater one in this case - where Holmes has exhibited behaviors that are sometimes inconsistent with Colorado's two-pronged legal definition of insanity, let alone the common sense definition.

In answering their burden, prosecutors are likely to point to the fact that Holmes planned this crime in explicit detail, performed reconnaissance on the theater, accumulated weapons and set up traps at his home as reasons why he should be declared "sane." But getting the jury to weigh those points and look beyond the common sense definition of "insanity" will be a huge challenge.

Throw in the fact that this is a death penalty case, and obtaining a fair jury becomes an even greater problem.

In fact, Colorado District Attorney George Brauchler rejected a guilty plea in exchange for a sentence of life in prison without parole, saying that in this case "justice is death."

Given that goal, Brauchler had better hope he finds jurors willing to hand down the death penalty against a defendant they most likely regard as insane. Otherwise - after months of jury selection, many more to follow for the trial and vast dollars spent - the degree of justice he seeks will have slipped his grasp.  

Heather Hansen is a partner in the O'Brien and Ryan law firm who has been named one of the 50 top female lawyers in the state by Pennsylvania Super Lawyers. Heather is also a national television and radio legal analyst and journalist who has appeared extensively on CBS News, Fox News, Fox Business Channel, Fox.com, CNN, HLN and Sirius XM radio. Her writing has appeared in Law360 and she has co-authored two chapters in medical texts regarding medical malpractice litigation. Follow her on Twitter at @imheatherhansen.