Life imprisonment not considered justice for Parkland victims' relatives

Nikolas Cruz, the troubled individual who shot and killed 17 people at a school in Parkland, Florida in 2018, has been handed a sentence of life imprisonment with no chance of parole.

You'd think this was an acceptable outcome to the trial, and that the grieving relatives would have some sort of closure after such a horrific incident.

However, to a person, or at least to those whose reactions have been reported in the press, those relative are absolutely incensed that Cruz did not get the death penalty, which the state of Florida still allows. Apparently, the jury did want to condemn the shooter to death, but Florida's legal system requires a unanimous verdict on at least one count, but they were forced to admit to mitigating factors that were not outweighed by other aggravating factors, and so they were not able to specify death, just the lesser penalty of life imprisonment without parole. (Apparently, just three of the twelve jurors voted against the death penalty, mainly because they believed that Cruz was mentally ill, but that was enough to kibosh the unanimous vote.)

Obviously, I've never been on that position, but I find it interesting that so many of the victims' relatives did not feel that this amounted to justice for them. The fact that the shooter would be locked up for the rest of his life, unable to participate in the world and unable to perpetrate any more crimes, did not even register with them. Nothing else but death would do. 

I don't know how common this kind of "eye for an eye, tooth for a tooth" attitude is in the wider public, or whether it is different in states and countries that do not allow a death penalty (about two-thirds of the world's countries, and not quite half of US states). It brings into question the whole problem of what constitutes justice for a crime.