Killing the man would solve nothing. In fact, the jury convicted him of involuntary manslaughter, which is not a capital crime anyway.

I fail to see how a 30-year sentence for a double murder is an appropriate sentence, nor how the Idaho Department of Justice could shave off 8 years for good behavior, especially since he took part in a jailbreak. But the sentence itself was delivered by the jury, who thought it wasn't murder. From the article:

Jury foreman Milo M. Moore, a retired shopkeeper, said Dallas might have been freed outright if he hadn't used his .22 caliber rifle [to polish off the officers by shooting each of them in the head after inflicting chest wounds with a handgun. -- MA]. Moore said testimony about Pogue's reputation as a tough-guy lawman influenced the verdict.

"We felt it was self-defense up to a certain point," Moore said in a recent interview. "Had he not shot them in the head, it would have been a different verdict."

Innocent by reason of self-defense, maybe. :/

Nope, this can't be laid at the feet of liberals who don't like capital punishment. It belongs to Idaho citizens who don't like lawmen.