Lorelei Guillory’s six-year-old son Jeremy was murdered by one of my clients, Ricky Langley. I was working for a charity in Louisiana at the time, and I was preparing for his trial when I met Lorelei. She was obviously heartbroken at the death of her child, but more than anything else she wanted some understanding of what had happened to him and why.

This was difficult for me to explain. Ricky was – and indeed still is – one of the most profoundly schizophrenic people I have ever known.

Before he was born, Ricky’s own five-year-old brother, Oscar Lee, was killed in a car accident when his drunken father, Alcide, drove off the road into a telephone pole. Bessie Mae, Ricky’s mother, was badly injured. Bessie was in a full length body cast when, unknown to the doctors, she became pregnant with Ricky.

Ricky, the foetus, floated in waters laced with narcotic medications, exposed to his own private Hiroshima through his mother’s regular X-ray examinations. When, five months on, the doctors finally figured out she was pregnant and cut off her cast, her bloated body gushed out. Bessie wanted to abide by the doctors’ advice to abort, but her husband, a staunch Catholic, refused to countenance it. He wanted a son to replace the tousle-haired Oscar Lee.

One of the difficulties when presenting an insanity defence is how to describe to presumably rational people (normally the judge or jury, but in this case the victim’s bereaved mother) what is going on inside the head of a deeply disturbed person. Ricky genuinely thought he was strangling his schizophrenic alter ego the dead Oscar Lee. Ricky thought Oscar Lee, his “tormentor”, was somehow the cause of his pedophilia.

It is a common misunderstanding to think that intelligent people cannot be insane. My father – who I loved dearly – was a brilliant graduate of Cambridge University, yet he was sometimes profoundly psychotic. Likewise, Ricky was intelligent, and he knew we thought him very ill, yet his mind was his reality. He understood enough about his pedophilia to loath himself far more than our venomous society could. All he wanted in life was to be committed permanently to a mental hospital – that, and to say sorry to the Jeremy Guillory’s mother.

It took astounding courage, though, for Lorelei to go down to the parish jail in Lake Charles, Louisiana, and sit face-to-face with the man who had killed her child, while he tried to explain the unfathomable way in which the child died.

And yet she did this. She believed him, and announced, “Ricky, I’m gonna fight for you.” She decided that she wanted to testify for him, not just that he should not be executed but that – because he was insane – he should not even go to prison.

I asked her one question in court: “Do you have an opinion as to whether that guy over there, who killed your son, was mentally ill?”

Her response was remarkable: “Yes, as a matter of fact I do. I think that Ricky Langley has been crying out for help since the day he was born and, for whatever reason, his family, society and the legal system has never listened to him. As I sit on this witness chair, I can hear the death throes of my child, but at the same time I can hear that man crying out for help and yes, I think he was mentally ill when he did it.”

That was astounding compassion. She indicated that she wanted him in a mental hospital rather than a prison. And, with those words, what had been the hardest closing argument in a capital trial I had ever faced suddenly became very easy – I just quoted her, and the jury nodded vigorously.

I have a seven year old child, Wilf. When he gets upset at one of his primary school friends, just like any parent, I try to show him the path to compassion. Lorelei did not just teach this, she lived it. In some ways, properly interpreted, Islamic law allows more space for victims to show mercy than Western tradition. Bizarrely, many governments (the omnipotent teachers) harp on about vengeance, with little reference to kindness. Indeed, the District Attorney prosecuting Ricky Langley tried to have Lorelei’s second child taken from her, labeling her an “unfit mother”, because she would not go along with his effort to have Ricky executed.

Lorelei’s story is going to be told in Islamabad this Saturday, and I am pleased to be in Pakistan to discuss it afterwards. The play is told entirely in Lorilei’s own words – written by Australian author, Tom Wright, when he was working as Cate Blanchett’s deputy in Sydney. It had a good run in London (I saw it several times there), and it explores what the death penalty can do to the people it supposedly protects. It lays the rawest of emotions bare, in words that resonate across the cultural divide.

Lorilei’s struggle has not been black and white: she sees a distinction between forgiveness and mercy. She cannot bring herself to forgive Ricky, but she did vehemently oppose his execution.

To Lorilei, it was vital that no other child should face harm, and she was comforted by the fact that Ricky agreed with her. Ricky signed an agreement requesting that he be hospitalised forever, as he wanted to become a sort of laboratory animal, studied so that future generations “can avoid another me.” Ultimately, then, she did not even want Ricky to go to prison, but rather spend the rest of his life in an institution where he could be understood and treated.

At her request, I asked Lorilei only one question during the trial: “Ms Guillory, do you have an opinion as to whether Ricky Langley was mentally ill at the time he killed your child Jeremy?”

Her answer was the most powerful moment I have experienced in a courtroom in more than thirty years of practice: “Yes, as a matter of fact I do,” she replied. “I feel like Ricky Langley has cried out for help many, many, many times. And for whatever reasons, his family, society and the system have failed him. I feel like he is sick. And even as I sit on this witness stand, I can hear my child’s death cry. But I too can hear Ricky Langley cry for help.”

Ricky was acquitted of first degree murder but his (and Lorilei’s) battle was not over, as the prosecution still found a way to send him to prison for the rest of his life. We got that conviction overturned, and the next one they imposed. Today, we are still working for justice, twenty years on.

In the United States, the criminal justice system is designed to inspire victims towards revenge. We are told that to try to understand a criminal is to pamper him. This is a desperately short-sighted approach for all concerned. As Lorilei learned, vengeance does not salve wounds, but makes them fester. She who hates becomes twice the victim.

The criminal justice system in Pakistan is rooted in something very different to an American gunslinger mentality, since in a murder case the family of the victim may always show mercy. Yet we often import the wrong lessons from the United States: populists shout loudly for vengeance, and the moral and Islamic principles behind a victim’s rights are often forgotten amid sensationalist newspaper stories.