Twelve years ago a Texas mother learned her 4-year-old daughter Ella had been brutally murdered.
The person who murdered Charity Lee's child wasn't a serial killer or known criminal.
It was her 13-year-old son, Paris Bennett.
Ella was stabbed 17 times and strangled by her sibling while she slept in her bed. Paris had convinced their babysitter to go home and later phoned 911 to confess to the murder.
He confessed he did it to get back at his mother.
ITV presenter Piers Morgan interviewed the now 25-year-old Bennett in a jail in Texas where he is serving 40 years behind bars.
Having spent almost half his life in prison, he will soon be eligible for parole.
With an IQ of 141, Bennett qualifies as a genius. Less than a quarter of one per cent of the world's population has that level of intelligence.
As Morgan wrote in his story for Daily Mail, Bennett is also a psychopath, "someone who has been formally diagnosed as a psychopath by medical experts".
Echoing famous scenes from The Silence of the Lambs, Morgan met Bennett in a secure room behind reinforced glass with heavily armed guards standing by. He was told he could not speak to the killer face to face.
"Why not?" Morgan asked.
"He's too dangerous," came the reply.
Morgan wrote: "True psychopaths have a chronic mental disorder that manifests itself in a number of personality traits including amoral or antisocial behaviour, extreme egocentricity, a lack of ability to love or establish meaningful relationships, and no sense of guilt, shame or embarrassment.
"Psychopaths can also be quite terrifyingly violent. Paris Bennett ticks every box."
The facts of the case are chilling.
When he was 13, Bennett says he decided to punish his mother Charity for perceived wrongs. He planned to kill her. But instead decided to kill his 4-year-old sister Ella, effectively doubling the impact - one child dead, the other in prison.
While mother Charity was at work in a local bar, Bennett put his plan into action. He told the baby sitter to leave early, then calmly walked into his sister's bedroom and began ferociously attacking her.
Bennett then called a friend on the phone and talked for six minutes before calling the police, who came and arrested him.
Lee told Morgan: "If Paris had killed me as he originally intended, I'd have only suffered for a brief few moments.
"But by killing Ella instead, he knew he was sentencing me to a lifetime of suffering."
Incredibly, Lee says she has forgiven her son and visits him regularly. But she fears that if he is granted parole, he will torment her all over again.
When asked about her son, Lee told Morgan: "He's human. He'll be nice, personable, polite. Paris is very charming when he wants to be. I mean, he's a psychopath."
As Bennett walked into the secure room he announced, "Hello everyone".
"Since this is going to be done for ITV, would you like me to speak in the Queen's English?" he asked Morgan.
"Why are you doing this interview?" Morgan asked Bennett. "To show people that I am not a monster or villain," he replied.
"Can you rationalise or explain what you did to your sister?" Morgan asked.
"I can't easily explain everything. I think that's been one of the biggest challenges for other people through the years, because no one likes to be confused. No one likes to be bewildered. We like… easy answers."
Morgan asked why he had so much fury.
"For many years, there was just this hot, flaming ball of wrath in the pit of my stomach and it was directed at my mother," Bennett said.
"And one of the reasons why I chose to kill my sister and not someone else is because I knew that by doing that I could hurt my mother in the worst possible way, because I had always known, as a child, that the most devastating thing to my mother would be the loss of one of her children, and I found a way to take away both her children in one fell swoop.
"Part of me loved my sister and would have turned the world upside down for her." But there was a part "wounded, twisted, dark… the part that had been in pain for so long".
"Misery loves company," he said.
"I love her [Ella] with every fibre of my being."
When asked by Morgan if he knew what love is, Bennett replied: "I don't know how to answer that question. It's not simple. I can't just point at something and say, 'OK, that's love, I recognise it and feel that'."
Bennett was then asked if he would kill again.
"The only person I'm dangerous to is myself because the very moment I feel the chains slipping and the bars bending, the very moment I detect that dark part of myself coming back out again, I would remove myself from the equation.
"Every single person walking around has it in him or her to commit murder. Margaret Atwood once wrote that if we were all on trial for our thoughts, we would all be hanged."