It ought to be possible to measure whether the death penalty actually makes victims' families feel better

You often hear it argued that the families of victims will not "find peace" until the murderer/rapist/etc. is executed. Certainly, victims' families feel an intense burning desire for retribution. I would too, I am sure! But does it actually make them feel better? As one who does not really believe in the idea of "closure", I am skeptical... But it just occurred to me while reading the recent Hitchens piece on the topic that we ought to be able to measure this.

One problem might be getting a large enough sample size, since there are only so many people executed per year, and you need to get the families to agree to do a series of questionnaires. And you need to have the first questionnaire administered before anybody's been executed, and you don't know for sure whether the execution will be granted, etc.

Anyway, I figure you want to have three cohorts (and two of them are indistinguishable before the end of the study, so it's tricky). One is families of murder victims where the perpetrator will certainly not be executed because the state does not have the death penalty. Another is families of murder victims where the death penalty was sought and granted, and the third is families of murder victims where the death penalty was sought but ultimately denied. You take various measurements of their psychological state at the outset of the study, then at various intervals later (e.g. 1 year later, 3 years, 5 years, 10 years, or something), and also immediately after the execution for families in the relevant cohort.

In this fashion, we could see whether seeking and getting the death penalty actually does make victims' families feel better. My hypothesis would be that we'd expect to see a short-term bump immediately after the execution, but no long term differences -- and I would not be surprised if families in the cohort where execution was sought but denied might do worse even in the long term. I would love to see it measured...