A Nottingham man jailed for murdering a woman by setting her house on fire has had his conviction overturned.
William Rowbotham, 20, was found guilty of murder and arson with intent to endanger life over the fire in June 2009, in which Susie Southern died.
London's Appeal Court quashed the verdicts, ruling they were "unsafe" because of his state of mind.
The convictions were substituted for manslaughter and arson being reckless as to whether life is endangered.
Rowbotham had also been found guilty of burglary, but the High Court removed that conviction.
After his trial at Nottingham Crown Court in January 2010, he was given a mandatory life sentence for murder and the judge ordered he serve a minimum of 14 years before being considered for parole.
The court heard Rowbotham, who has learning difficulties, drank vodka before setting fire to bins outside 54-year-old Mrs Southern's home in South Snape Close, Bulwell.
He then put pieces of wood inside the bins and pushed them against the front door, blocking the grandmother's exit from the house.
Jurors heard from defence experts about his mental state, with a psychiatrist saying his "poor intellectual functioning" meant he had not been able to think through the consequences of his actions.
At the High Court on Tuesday, Peter Joyce QC, for the Crown, argued there was enough evidence he was aware of his actions and had formed the "necessary intent" to be guilty of murder and arson with intent.
But Lord Justice Laws, sitting with Mr Justice Wilkie and Mr Justice Nicol, said the "wholly exceptional" circumstances of the case meant it wasn't one in which a jury could have convicted Rowbotham of the offences with which he was charged.
He said: "The appellant was an 18-year-old boy with an interest in fires, his mental capacity was extremely modest and he was very drunk on the night in question.
"In our judgment, arrived at not without considerable anxiety, this is a case in which it would have been right to invite the trial judge to stop the case after the defence expert's evidence.
"In those circumstances, which we consider wholly exceptional, we will allow the appeal against conviction."
The judges adjourned the case so probation and psychiatric reports could be obtained before they consider what sentence should now be imposed on Rowbotham.