In her final moments, Nancy Bishop Langert somehow summoned the strength to crawl across the basement floor. There, lying beside her husband, she used her index finger to write a message – in her own blood.

At the trial of the 16-year-old high school student who shot and killed the young couple – and their unborn child – a desperate defense lawyer suggested that perhaps Mrs. Langert was trying to spell out the name of a killer other than his client.

Langert’s sister, Jeanne Bishop, knew better. The message, the symbol of a heart and the letter “U,” is exactly how Nancy signed her notes and holiday cards.

“It wasn’t until a week later that the police told us about this message,” Bishop said in a telephone interview. “The person they told was my mother… She started crying and she said: ‘It’s true isn’t it, that love is stronger than death.’ ”

To Ms. Bishop and the shattered members of her family, that final scrawled message was an expression of pure, selfless love, produced in the midst of what must have been unimaginable terror, grief, and sorrow.

Instead of dwelling on that, Bishop says her sister somehow rose above it to deliver an indelible healing message that Bishop says has transformed her life, and shaped her perspective about unspeakable crimes committed by young teens.

Jeanne Bishop’s story is among 11 testimonials contained in a friend-of-the-court brief filed in a US Supreme Court case set for oral argument on Tuesday.

At issue is whether the high court should extend a 2012 ban on mandatory sentencing laws that automatically send juvenile offenders to prison for the rest of their lives with no possibility of parole.

Three years ago, the Supreme Court declared that mandatory life sentences were unconstitutional for those who commit their crimes at age 17 or younger.

The court reasoned that such young offenders had not yet fully developed into adults and that it would be unconstitutionally cruel to punish them for the rest of their lives for the reckless and impulsive acts of an immature mind.

The decision invalidated sentencing statutes in 28 states and the federal government. But the court left open whether the decision should apply retroactively to those inmates already serving mandatory life terms without parole for crimes committed while juveniles.

There are more than 2,500 inmates in the US currently serving life-without-parole sentences for crimes committed as juveniles. All but 400 are mandatory sentences.

The question is what should happen in those cases.

Since the high court’s 2012 decision, 14 state supreme courts have ruled that the decision is retroactive, while seven have ruled that it should not be applied retroactively to those already serving their sentences.

The case of Henry Montgomery

The issue arises in the case of Henry Montgomery, a 69-year-old inmate in Louisiana serving a life sentence with no possibility of parole for the 1963 shooting death of a deputy sheriff in East Baton Rouge.

Mr. Montgomery was 17 when he killed Deputy Charles Hurt. At his first trial, Montgomery was convicted and sentenced to death, but that conviction was overturned because of the poisonous racial atmosphere in the community prior to and during the trial.

At a second trial, Montgomery was also convicted, but this time the jury did not return a death sentence. Instead, he received a mandatory sentence of life with no possibility of parole.

In its 2012 decision invalidating mandatory life sentences for juvenile offenders, the Supreme Court said that judges cannot automatically sentence a juvenile to spend the rest of his life in prison without first conducting an individualized examination of a variety of potential mitigating factors related to that young offender.

Lawyers for Montgomery argue that since a youth-specific examination never took place in their client’s case more than 50 years ago, his sentence is now unconstitutional. They are asking that he be re-sentenced.

Lawyers for Louisiana counter that Montgomery is not entitled to a new sentencing hearing. At the time it was imposed in the 1960s, Montgomery’s sentence was constitutional, and under the high court’s new youth sentencing regime, sentences imposing life without parole are still constitutional as long as they aren’t imposed automatically, lawyers for the state say.

The lawyers add that a re-sentencing in the Montgomery case would pose severe difficulties.

“The sentencer would have to determine whether Montgomery’s youth should have impacted the sentence he received for a crime he committed a half century ago,” Washington lawyer S. Kyle Duncan wrote in the state’s brief.

He noted that, as near as he could tell, everyone involved in the Montgomery trial – except Montgomery – is now dead.

“If those conceptual and practical obstacles were not enough, one must also consider the effect of the resentencing process on Deputy Hurt’s surviving children, who would be forced to publicly relive the anguish of having been deprived of a father for the better part of their lives,” Mr. Duncan said.

In a brief filed on behalf of Deputy Hurt’s daughter, Becky Wilson, the National Association of Victims of Juvenile Murderers declared that making the Supreme Court’s 2012 decision retroactive would be traumatic, unfair, and would deprive surviving family members of what they thought was finality.

“When a juvenile murderer killed their loved one, the surviving members were traumatized,” the brief says. “Reopening these cases for resentencing will retraumatize them, forcing them to relive the events that traumatized them in the first instance. These surviving family members deserve no less respect than the juvenile murderers.

The brief says that Ms. Wilson has forgiven Montgomery. But it adds that Wilson believes forgiveness is a personal issue and that there is a societal interest that people pay the consequences for their actions.

At the time of her father’s killing, Becky was 9 years old, her brother was 11, and her sister was 6.

“Charles Hurt did not get the chance to be a father to a family that needed him. He did not meet any of his grandchildren. He received few of the gifts and none of the satisfaction that comes from having a family grow up well.”

“Montgomery’s actions took that away from Charles Hurt and from his family. The consequences that have followed are Montgomery’s responsibility,” the brief says.

'I did it for Nancy'

Like Hurt’s children, Bishop is also a surviving family member. But she has decided to follow a markedly different path in the aftermath of her family’s devastating tragedy.

It stems in large part from the message of love her sister left at the crime scene in April 1990 in the basement of her Winnetka, Ill., townhouse.

“At first I thought it was the kind of love that is reserved for the good people, the people around you,” Bishop says. But as she kept returning in thought to that heart-shaped symbol, she said her concept of love began to expand.

“I realized that love was for the whole world,” she says.

Through her religious faith, Bishop sought to make peace with her sister’s death and with her killer. “I did it for Nancy because I didn’t want her memorial to be hatred and vengeance,” she says.

She became an active worker in campaigns to end gun violence and ban the death penalty. But for more than 20 years, Bishop refused to speak the name of the person who killed her sister and brother-in-law, even after he was sentenced to life in prison without parole. Hers was a targeted concept of forgiveness.

“It wasn’t about him in any way. He hadn’t asked for it. He didn’t deserve it. He had never taken any responsibility or shown any remorse,” she says.

“So it wasn’t until later, over time, through the wise counsel of a number of different people along the way that I came to see that it did have to be about him, too,” she says.

She says she came to see the killer as a child of God, someone capable of redemption. “To just throw him away does nothing to really honor the memory of my sister or redeem her death.”

Bishop says she’d been waiting for more than 20 years for the killer to apologize. Eventually she realized that she would need to go first. “So I wrote him and I said I forgave him a long time ago and I never told you and I’m sorry.”

David Biro, the convicted killer, responded immediately with a 15-page handwritten letter.

“He wrote me back and confessed to the crime for the first time. He said, ‘I know you and your family have waited a long time for me to say this and I won’t make you wait any longer. I did kill your sister and her husband and I am so sorry. If I could take it back, I would.’ ”

The story might have ended right there with a clear expression of remorse from Mr. Biro. But Bishop doesn’t do anything halfway.

She decided to go see him, face-to-face, in prison. That was in 2013. She’s been visiting him every two months ever since.

Most of that visiting time is spent talking about her sister, her brother-in-law, and the family they wanted to raise. Bishop tells Biro, now 41, about how her sister and her husband adored each other and wanted to grow old together. She talks about how happy they were.

“He said to me the other day, the more I get to know you, the worse I feel about what I did,” Bishop says. This is part of her plan. “Through me, he got to know Richard and Nancy.”

Bishop believes remorse can be an effective agent of healing. “I want that remorse to live in him and motivate him,” she said.

“I said this to him. I looked into his eyes and said: ‘Every day you wake up and open your eyes and see this world and draw a breath is a day that they didn’t get to have. Every opportunity you have to do good for another person, to influence events around you, that’s something they didn’t get to do. You are living for them now, your life is not your own.' ”

Bishop says she realizes that many other victims of heinous juvenile crimes disagree with her approach. They are angry and hurt and insist on strict justice. They want retribution.

“I can only say this was my journey,” Bishop says. “This has been incredibly healing for me to see this person who took my sister’s life feel regret, show his pain when I talk to him about the person whose life he took. To know that he is becoming a better person, that there is some good that is coming out of this tragedy.”

She adds: “It’s been good for me. It is good for him, and I think ultimately it will be good for all of us. I think that is the only way we can end up whole.”

Bishop has more than a passing acquaintance with the criminal justice system. She works as a public defender in a Chicago suburb. She has also written a book about her transformation. It is called “Change of Heart: Justice, Mercy, and Making Peace With My Sister’s Killer.”

When the case is over

As far as the Montgomery case, Bishop says she hopes the justices reject “this notion that we can decide who someone at age 14, 15, 16 will be when he is 50, 60, 70 years old.”

Bishop acknowledges the desire for finality in the aftermath of a horrible crime, but that there are different ways to achieve finality.

“My argument is that not every victim’s family member wants the harshest possible sentence. Not every victim’s family member finds healing in endless retribution,” she says.

“There is another route to finality,” she adds. “When this person who did this terrible act has shown remorse for that act, has done everything he can to express sorrow, has done everything he can to rehabilitate, is ready to rejoin society, and when he walks through those prison gates into freedom back into the arms of his community, that is finality, that is when the case is over.”