Viewers who saw the Investigation Discovery documentary The Family I Had last month witnessed a true crime story almost too horrific to contemplate. A decade ago, then 13-year-old Paris Bennett killed his four-year-old sister, Ella, with a kitchen knife.

The documentarians interviewed Paris, now 24, in the Texas prison where he’s serving a 40-year sentence — the state’s maximum sentence for a juvenile murderer — and the New York Post recently published an interview his mother, Charity Lee. Just after midnight on Feb. 5, 2007, cops found Charity at a Buffalo Wild Wings near Abilene, TX, where she waited tables.

“[The police] told me that my daughter had been hurt,” she says in the film, remembering that fateful night. “And I was saying, ‘You need to take me to Ella now,’ and they were like, ‘You can’t go… She’s dead.’

“And that made no sense, because I knew that I’d left her at home with a babysitter and her brother, so I said, ‘Is my son OK?’ And they said, ‘We have him.’ … That’s when everything stopped making sense.”

Around 10 p.m. that night, Paris had convinced that babysitter she could go home. Detectives say Paris then beat, choked, and repeatedly stabbed Ella. Afterwards, he spent six minutes on the phone with a friend and then waited another two minutes before calling 911.

“He pretended to follow the dispatcher’s directions and do CPR,” Charity says. “But that was all a lie.”

Paris later told investigators he woke up that morning with an urge to kill someone. He even planned on killing his mother when she got home from work, wanting to punish her for relapsing on heroin.

“He said the first reason he didn’t go ahead with it was because it was a lot harder to kill someone than he thought,” Charity says. “The second reason was the realization if he’d killed me, I only would have suffered for five, 10, 15 minutes. But, if he left me alive [without Ella], I would suffer for the rest of my life.”

“The only regret I’ve ever had about my own personal behavior is my relapse,” she adds. “The fact is, it made him angry and he chose to handle it that way [by killing Ella].”

Paris was a gifted child with an IQ of 141, and after his sentencing, Charity was told he’d be classified as a sociopath. He himself revealed he had had murderous impulses since the age of 8, but in his adult years, he has refused psychological evaluations.

“I chose to do my crime and I take full responsibility for my crime,” he told the documentarians. “And I wouldn’t say there was a predisposition to what happened. I’m not insane, and I don’t suffer from any mental illness.”

Charity calls Paris “manipulative” and “narcissistic,” but she still puts her love for him above her anger. “I have forgiven Paris for what he did, but it’s an ongoing process,” she tells the New York Post.

Today, she lives in Georgia now and has welcomed a third child, a four-year-old named Phoenix, but she still travels to Texas to visit Paris whenever she can. Paris has written letters to his brother, but Texas forbids the inmate from having minor visitors due to the severity of his crime.

In 2011, Charity started the ELLA Foundation — “Empathy, Love, Lessons, and Action” — a nonprofit that assists those in the criminal justice system and those touched by trauma. “On the night that Ella died, I vowed to do something meaningful in her memory,” Charity says. “It also gave me a place to direct my rage, other than at my child.”