It took the jury of seven men and five women just over seven hours of deliberation to find Lindsey Fletcher guilty of murdering her step-grandfather, Michael Eaton, 72, by a majority of 10 to 2.
Fletcher, of St James's Street, Hyde Park, pleaded guilty to the manslaughter of Mr Eaton prior to the beginning of the six-day trial, but denied murder.
The judge, Mr Justice Nicholas Lavender QC, sentenced Fletcher to life imprisonment, to serve a minimum-term of 13 years, at the conclusion of the trial at Sheffield Crown Court on Monday, June 18.
Mr Justice Lavender told her: "On Christmas Day last year you were in the flat of your step-grandfather. You had been taking drugs, crack cocaine and heroin, and were in the kitchen when you hit him repeatedly about the head with a meat cleaver. You hit him six times, breaking his nose, you picked up a steak knife and stabbed him 30 times in the back of the head, and 90 times in the back."
He added: "The jury didn't have to find that you intended to kill Mr Eaton [only that you intended to cause him serious harm] but I'm sure that you did. That's clear from from what you did to him, and also from what you said to a number of people in previous months."
After killing Mr Eaton, Fletcher, aged 39, cut his clothes off with scissors and doused him with bleach.
She then disposed of his clothes at a nearby waste site and in the river, while her 12-year-old daughter was with her.
Another of his step-granddaughters discovered his body at his home in Low Road, Balby on Boxing Day last year.
Mr Justice Lavender said he accepted Fletcher's assertion that Mr Eaton had sexually abused her when she was aged between five and 11-years-old at the home he shared with her grandmother, and that this had led to her developing an addiction to Class A drugs as a teenager which had plagued her throughout most of her adult life.
He told Fletcher that he regarded the abuse she suffered at Mr Eaton's hands as a 'significant mitigating factor'. Fletcher never reported the sexual abuse to the police, the court heard.
Despite argument to the contrary from lead prosecutor, Dafydd Enoch QC, during the trial, Mr Justice Lavender said he also accepted Fletcher's claim that Mr Eaton continued to sexually abuse her in the two years that she lived with him prior to his death, and that his attempt to sexually assault her on Christmas Day is what sparked the fatal attack.
"What you did went way beyond what any woman of your age, who was sober, who had a normal amount of tolerance and self-restraint would have done in the circumstances," added Mr Justice Lavender.
Despite evidence from her computer suggesting Fletcher had been researching methods of poisoning, Michael Hayton QC, defending, told the court that Fletcher had not planned the 'frenzied' attack, something he said was further supported by her using items that were close to hand as weapons.
Speaking after the sentencing hearing, Detective Chief Inspector Steve Handley, the Senior Investigating Officer said: “Mr Eaton was found with in excess of 120 stab wounds to his upper body, including to his face, head and neck.
“After he was killed he was stripped naked and had bleach poured over him in an attempt to conceal evidence. “Through extensive forensic work, CCTV enquiries and speaking to associates and extended family members of Mr Eaton, Fletcher was quickly identified as a suspect and subsequently arrested two days later.
“This investigation without doubt required significant resourcing, with expert forensic examination being undertaken, including specialist underwater search officers who searched the river Don at Balby over a three-week period, looking for items Fletcher had discarded after killing Mr Eaton. “Throughout those searches divers were able to recover Mr Eaton’s clothing, including his jumper which was covered in holes showing exactly where he had been stabbed. “His walking stick, believed to have been used in the attack, was also recovered. The knife she used to stab him has never been recovered.
“Fletcher had previously spoken to friends of her hatred for her step-grandad, even going as far to say she wanted him dead, and as part of the investigation it became apparent she had researched the most hazardous types of poison to kill someone online.
“During the four day trial, Fletcher revealed that her hatred towards Mr Eaton had stemmed from prolonged sexual abuse by him, from her childhood into adult life, a fact she had never reported to the police.
“We were able to bring a strong case against Fletcher, to hold her to account for taking Mr Eaton’s life, and I’m pleased that she has today been found guilty of killing him and has been jailed for a significant amount of time.”