Soon after police arrested the killer who blasted his father with a shotgun, in front of his mother, in the doorway of their New Hampshire home, Renny Cushing ran into an old family friend at the neighborhood grocery.

“I hope they fry the bastard, so you and your mother can get some peace,” the friend told Cushing, who understood the friend was “just trying to give me some comfort.’’

Most of us simply assume that families of murder victims want the death penalty, even need it, Cushing said, to find comfort or peace or that overused cliché, “closure,” which really doesn’t exist. And most of us, he said, assume that families of the murdered who oppose the death penalty are either saints or misguided or perhaps deficient: maybe they didn’t love their dead mother or father or child enough to crusade for justice.

But Cushing, who not only lost his father but also a brother-in-law to murder, doesn’t see it that way. “A ritualized killing by public employees is not going to bring back anyone who’s murdered,” he said. Very likely it will leave the victim’s family not better off, but worse. That’s what he’s learned after 25 years of working with families of the murdered.

Call it the death penalty paradox:  the executions survivors want – particularly in the first weeks and months after the murders – can turn out not to ease their grief but keep them wrapped up, entwined, even entrapped by the minute particulars of the killer’s life — and fate.

Cushing spoke of all this Monday at a Boston forum during the death penalty phase in the trial of Boston Marathon bomber Dzhokhar Tsarnaev. It also coincided with testimony for the defense by Helen Prejean, the Roman Catholic nun and death penalty opponent who visited Tsarnaev multiple times in jail.

Although she told reporters she could not speak outside of court until after the verdict, Prejean has repeatedly said before – and detailed in her classic book, “Dead Man Walking” – what Cushing said: that executions typically fail to bring about what many hope for: a sense of justice. Instead, at a time when families need each other most, executions can divide brothers and sisters and husbands and wives between those who favor death, and those who don’t. They can turn families into unwitting pawns for politicians pushing a tough-on-crime agenda. They can also, as the parents of 8-year-old Marathon victim Martin Richard have said, delay a family’s ability to put the killer out of mind as death appeal after death appeal keeps him on TV and in the news, a death row celebrity.

Also at Monday’s forum was Robert Curley of Cambridge. His 10-year-old son Jeffrey’s horrific 1997 kidnapping and murder became a rallying cry for Massachusetts politicians hoping to whip up outrage and reinstate the death penalty. Curley said he got swept up in the furor as well. He told me how he’d imagine slipping a straight-edged razor past metal detectors and courtroom officers, then leaping over the banister and slaughtering his son’s killers before anyone could stop him. He said he felt an obligation to favor the death penalty since everyone around him assumed, like Renny Cushing’s neighbor, that he had to – for his little boy. “People would come up to me on the street, total strangers, and want to talk to about the death penalty.” It got pretty angry, crazy, out of control, Curley said, “like they wanted the death penalty for somebody who just spit on the sidewalk.”

When Curley began to think differently about executions – mostly because of injustices he witnessed in the criminal system – he was nervous about admitting it publicly. The pressure was huge. Was he disrespecting Jeffrey? Was he letting people down?

Bud Welch, whose 23-year-old daughter Julie Marie was killed in the Oklahoma City bombing in 1995, talked about similar pressures Monday. “How the court system’s cure-all was to get the death penalty for Terry Nichols and Timothy McVeigh (the bombers). How that was going to solve everything for me and the other family members. But I remember very clearly June 11, 2001. In Terre Haute, Indiana, when we took Tim McVeigh from his cage and killed him, what I learned was that I was re-victimized all over again. It didn’t solve anything. I struggled for many months after that and I guess my strong opposition to the death penalty is what it does and does not do for victim’s families, what it does to us as human beings.”

After a year of rage and “self-medicating with alcohol,” as Welch told me, “I decided I had to change my life and speak of tolerance and forgiveness. The death penalty is all about revenge and hate. And revenge and hate is why Julie and 167 other people are dead.”

Forums like Monday’s are nothing new. They often are scheduled around death penalty trials, like Tsarnaev’s. Welch, Curley, Cushing, and Prejean have spoken at many. I first met Prejean at a college near Boston months after Susan Sarandon played Prejean in the 1995 movie,  “Dead Man Walking,” which made Prejean famous.

That day Prejean spoke about the death penalty as a cancer that sickens everyone around it. The “strap down teams” at death penalty prisons who rehearse the killing drill: shackling the condemned in wrist and leg irons, walking him to the death chamber, tackling and subduing him should he resist. The guards retrieve the dead prisoner’s used soap and toothbrush from his cell to give to his family. One guard told Prejean it all became too much. He could not eat or sleep. Eventually, he quit his job.

Prejean also talked about the families who truly believed execution would relieve or at least diminish their anguish. Vernon Harvey, the stepfather of an 18-year-old who was raped and stabbed to death, watched Faith Hathaway’s killer die in the electric chair. But he felt little relief, and said the murderer didn’t suffer enough. A no-nonsense military man, Harvey then became a death penalty crusader, keeping vigils at every execution at the Louisiana State Penitentiary even as he grew sickly and needed a walker. But witnessing more deaths neither provided that elusive relief nor lessened his increasing anger. Instead, Prejean said, anger seemed to be what sustained him in his crushing grief. His wife and grown children became alienated from Harvey, who died of a heart attack ten years after he watched Faith’s killer die.

“We’re doing these killings for the politicians while they’re home asleep in their beds,” Prejean told me then. We’re selling to families the idea that a second, state-sanctioned murder can somehow fix the murder of the one they loved.  We’re telling them that executions are right and just and will help them heal. But none of it, said Prejean, is true.