system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why did it take 3 years to convict James Holmes of a mass murder that he clearly commited?
gpt
Because things *aren't* that clear cut.

Murder is a very specific charge (it requires killing that is premeditated, malicious and wilful). Even if you see someone kill another person, that doesn't mean that person is automatically guilty of murder. Could just end up as manslaughter. Or not guilty by reason of self defence. Or not guilty by reason of insanity. To prove whether it is one over the other, evidence needs to be gathered, witnesses need to be interviewed, psych profiles need to be made, examined, possibly redone. All of that takes a long time. And seeing as the US has double jeopardy laws - as in, you cannot be tried twice for the same crime - it is of the utmost important that this whole process is done carefully and that every little detail and fragment is looked at. Because if the prosecution fails and the guy walks away from this, they can never charge him for it ever again. Even if he admits to it later or other evidence comes out to prove it was him. Criminals have gone free in the past due to the prosecution bungling and rushing into a case with not enough or proper evidence. You really don't want to do that with a guy who is suspect of killing multiple people.

Add in a good dash of how backed up the court system is, the time it takes to find a good jury in cases like this (a jury should be unbiased, but that is hard to find when cases like this have been so hugely reported on in the news) and it should be clear why this all took so long.