Life/WMG

Crews is an alternate universe version of Vic (The Question) Sage
The similarities are rather impressive. Both fought crime, had a rather unfortunate incident, then discovered Zen and resumed crimefighting better than ever. Both are redheads. Both wear blue for crimefighting (The Question's blue suit matched by Crews' bulletproof vest). And both are impressively badass in hand to hand combat.
 * Don't forget their partnerships with non-white female (ex-)cops who serve as long-suffering straight man to their eccentricities and tend to deal with their own problems through alcohol and meaningless sex.

Crews never got out of prison.
He snapped while he was in solitary and the entire show is his hallucination. Think of all the crazy stuff that happens! Wouldn't some of it make more sense if you knew it was dreamed up by an insane man?
 * Life is weird. The focus around him does make a tad more sense, though. Still, this reasoning leads to everything being a hallucination of Tommy Westphail, and we don't want that.
 * It also leads to a crossover with Life On Mars, and that would be awesome.

Crews is related to Horatio Caine

 * The similarities in looks, personality, and mannerisms can't be a bizarre coincidence.

The first person Charlie killed was a prison guard
Not much of a guess. It's pretty implied. We know that he did something to a guard that makes other guards hate him forever afterward. We know that eventhough he was exonerated for murders on the outside, there were rumors of what he did inside. Charlie has said that "everybody breaks" and that the first kill makes you forget who you are and also that at one point even he wasn't sure he wasn't guilty. We also know that the first time Connie came to see him about an appeal, he wouldn't talk to her at all.

So, clearly, sometime in the first eight years of his sentence he broke, killed a guard, forgot who he was, started thinking he was capable of killing his friends eventhough he didn't remember doing it, and decided he belonged in prison. It had to his first kill or he would have built up a tolerance to those kinds of feelings. He was almost certainly in that "97%" before he went to prison.
 * See how he finally  What if he did the same to a guard: kill him without leaving any usable evidence, thus avoiding any legal punishment for his real murder, earning the hatred of prison guards while at the same time frightening them so much that they never tried to get revenge?