"Closure" is Hooey

Is there any evidence that executing murderers brings "closure" to the victims' families?

No.

Dahlia Lithwick:

To the extent the data on the needs of victims suggest anything, it says there is no magical solution, no one-size-fits-all mechanism to afford closure to the victims and survivors of violent crime.

She cites a study by law professor Lynne Henderson:

Looking carefully at the existing psychological data on the needs of victims, Henderson discovered a wide array of victim responses to tragedy, responses that differ from victim to victim and that change significantly over a victim's lifetime. "In light of the existing psychological evidence," Henderson concludes, "common assumptions about crime victims—that they are all 'outraged' and want revenge and tougher law enforcement … fail to address the experience and real needs of past victims."

The government really played up the "closure" angle in the trial and execution of Timothy McVay, allowing victims' families to watch McVay's death via closed-circuit tv. Those who opposed his execution were shrugged off:

The survivors of the Oklahoma City bombings who didn't want to see Timothy McVeigh executed were not permitted to offer victim-impact statements at his sentencing. As Bruce Shapiro pointed out in this 1997 essay in Salon, the terror trial that made "victim closure" a national buzzword was structured such that "any victim or relative who wanted to play a part in the sentencing phase of the trial first had to pass a death-penalty loyalty test."

There is a voice for sanity here, an organization of people who have become death penalty opponents after executions they sought did nothing to bring peace to their lives. They call themselves "Murder Victims' Families for Human Rights." They have just issued a report arguing that executions only create more victims:

Murder Victims’ Families for Human Rights released a report entitled “Creating More Victims: How Executions Hurt the Families Left Behind.” Families of the executed are victims, too, according to the new report, which draws upon the stories of three dozen family members of inmates executed in the United States and demonstrates that their experiences and traumatic symptoms resemble those of many others who have suffered a violent loss. “I don’t think people understand what executions do to the families of the person being executed,” says Billie Jean Mayberry, one of the family members featured in the report. Mayberry’s brother, Robert Coe, was executed in Tennessee in 2000. “To us, our brother was murdered right in front of our eyes. It changed all of our lives.”

There was an amusing moment in one of my family gatherings a few years back, when my conservative father and I started to argue about the death penalty and the whole room immediately emptied. But it turned out we had a lot of common ground, because we both think that if the state is going to execute people it should be for a state purpose, not because of some psychological crap about helping the victims' relatives.