Sarah Sands got 7½ years for the manslaughter of 77-year-old Michael Pleasted.
At her 2015 trial, it emerged Pleasted had 24 convictions for sex offences over three decades.
Mum-of-five Sarah, now 38 and out of jail, said: “I did what any mother would do because he did this to my son Bradley, my little boy.
“I never dreamt I’d be capable. I have no pride in it but at least I know he can’t hurt anyone else.
“I’m not a bad person but I know I did a bad thing. I’ve never denied that and I’ve been punished.
“I’d never kill again. I don’t see myself as a murderer.
“But I don’t regret what I did. I was a mum desperate to protect my children.
“I remember picking up a knife and I went to Mick’s.
“I wanted to persuade him to plead guilty so Bradley would not have to testify.
“Mick opened the door and smirked. He was cocky and abrupt.
“He wouldn’t listen to me. He was cold. A different man to the one who’d been my friendly neighbour.
“I poked him in his front with the knife and he grabbed me. I lost control. I couldn’t let anyone else get hurt, somebody had to protect people.”
‘Changed his name so he could attack kids’
Sarah had tried to get help after discovering her neighbour was an abuser.
But she claims police, social services and housing authorities failed to listen.
Pleasted’s council flat overlooked a playground and school in Canning Town, East London.
But nobody knew of Pleasted’s vile past because he had changed his name and his crimes pre-dated the sex offenders register.
This week it emerged hundreds of sex offenders have changed names via deed poll and failed to tell authorities.
In the most serious cases men barred for life from working with children have used their new identity to get jobs in schools and homes where they committed further offences.
Sarah said: “I had no idea who he really was. How could I? He had lied and changed his name so he could attack kids.”
So when Pleasted offered Bradley, then 12, a job in the shop where he was a volunteer in February 2014, Sarah thought it would be a good way for him to earn pocket money.
She said: “Mick was a role model. I’d take him meals and we’d chat.
“I had no reason not to trust him. I thought Bradley was safe.”
But Bradley soon lost interest in the job and weeks later Sarah was told Pleasted had been accused of molesting two children.
She said: “I knew the boys. I didn’t doubt a word they said. It was awful. They were 12, so young.
“Bradley said nothing had happened to him but he had to give a video statement to the police because he had worked with Mick
I begged social services for support. Nobody wanted to listen
Bradley and his siblings grew scared of living next door.
Sarah asked the police for help and they advised her to move.
She said: “We went to my mum’s two-bed flat. I thought it’d only be temporary. I asked Newham Council to move Mick. They said there was nothing they could do.
“They could rehome us but it would be away from London. I begged social services for support. Nobody wanted to listen.”
‘I felt sick and heartbroken’
In November 2014 Bradley broke down and said he’d been abused.
Sarah said: “I found him pulling out his hair, rocking, shaking and crying.
“He kept saying, ‘I should have told you before — that could have stopped him getting those younger boys’.
“He was attacked at the shop and his house. I felt sick and heartbroken.”
Bradley, now 19, is waiving his anonymity to speak of his ordeal.
He said: “I was too embarrassed to say anything at first.
“I didn’t want to get into trouble but I was having nightmares Mick would come after me.”
Sarah sat with Bradley all night as he explained how he had been groomed and abused.
She said: “I rang the police. They said they knew because Bradley had told them during his video evidence.
“I begged them to re-arrest Mick. He was back on the estate like nothing had happened and because he’d pleaded not guilty his victims, including my son, would be made to testify.”
That night Sarah took matters into her own hands.
So many victims wrote and said I’d done the right thing.
She said: “I drank two bottles of wine, returned to my old flat and knelt on the floor holding a photo of the kids, screaming.
“I hadn’t been able to cry before — Bradley was always around.
“The guilt I felt for not protecting him overwhelmed me. That is when I picked up the knife and went to Mick’s.”
Sarah stabbed Pleasted eight times with the 12in kitchen knife.
Twent-y minutes later she was caught on CCTV leaving the building.
She tearfully confessed, telling an officer: “Who houses a f*g paedophile on an estate?”
In September 2015 Sarah was convicted of manslaughter by reason of loss of control.
During her case at London’s Old Bailey, Pleasted’s child sex offences between 1971 and 1990 were revealed.
He’d changed his name from Robin Moult so authorities had lost track.
Sarah added: “I didn’t find out until I was in prison. I was blaming myself for allowing Bradley to spend time with him, when all along the authorities knew exactly what he was capable of and turned a blind eye.”
The judge said Sarah’s case was “truly exceptional” and took her position as a single parent into account when reducing her sentence from seven years to 3½.
But in January 2016 the sentence was more than doubled after the Court of Appeal ruled the original term was unduly lenient
Sarah spent almost four years in jail.
Her children lived with their nan but always visited their mum to keep up her spirits.
Sarah said: “Being away from them for so long was every mother’s worst nightmare but the officers treated me well.
“I told them exactly why I had done it, they knew the truth, so did the other inmates.
“A lot of the staff were mothers so could understand. So many victims wrote and said I’d done the right thing.”
Sarah was reunited with her family in August 2018 and has started a new life in Essex.
She is now writing a book called Loss of Control.