The 40-year-old woman, who cannot be named to protect the identity of the girl, wept as the jury at Leeds Crown Court found her not guilty. Another daughter was also cleared of perverting the course of justice.
During the trial the court was told the mother had kept a diary of hate in the weeks running up to the killing. In January of last year she wrote: 'He is dead when I see him.'
Another entry stated: 'The only reason I have not killed him is because I would end up inside and my daughter would be worse off.' And another said: 'As God as my witness I want to kill him slowly and painfully. I want him to suffer a million pains.'
She is also alleged to have told a friend while police were investigating the sex abuse allegations against John Lockwood: 'If he walks he will be walking with a knife between his legs. I am not going to kill him. I will get him where it hurts.'
The court was told that, in a phone call to Mr Lockwood, she told him: 'You pervert, you are going to prison. You know what they do to people like you when they are in prison. I hope you suffer.'
But last May, when she heard Mr Lockwood was not to face charges, she confronted him at his home in Wakefield, West Yorkshire.
The woman told the court she accidentally stabbed Mr Lockwood in the chest when she tried to smash his car window with a knife. She claimed that, after shattering the glass, her swing followed through and the five-inch blade plunged into his chest. She said she then aimed three more stabs at his groin before leaving. Mr Lockwood staggered out of the car, collapsed in the hallway of his house and died shortly afterwards.
The four-year-old girl had claimed, in interviews with the police, that Mr Lockwood had sexually assaulted her. During the trial the court heard there were also allegations of sexual abuse made against Mr Lockwood in the 1980s.
The mother had pleaded not guilty to murder and her 20- year-old daughter not guilty to perverting the course of justice. The mother, who had clutched a photograph of her young daughter throughout the trial, said as she left the court: 'I am over the moon. Now I just want to get home and see my daughter.'Reuse content