A drug user who strangled his grandmother and drowned his aunt in a bath in a "savage and brutal" double-killing has been jailed for life with a minimum term of 15 years.
Christopher Whelan, 21, armed himself with an axe and a pen knife during the killing of Julie Hill, 51, and 75-year-old Rose Hill after cannabis use "exacerbated" his violent thoughts linked to an obsessional disorder.
Nottingham Crown Court was told Whelan, who admitted manslaughter on the grounds of diminished responsibility, heard the voice of "Satan" directing him as he killed the victims at his aunt's home in Shirebrook, Derbyshire.
Passing sentence on Whelan, of Dransfield Road, Crosspool, Sheffield, High Court judge Mrs Justice Carr said the last minutes of both victims' lives must have been "terrifying, bewildering and agonising".
The judge told Whelan: "This was very serious offending involving the brutal death of two innocent women.
"They died in the most horrific of circumstances at the hands of a grandson or a nephew. I have no hesitation in concluding that you pose a significant risk to members of the public of serious harm.
"Both consultant forensic psychiatrists (acting for the prosecution and the defence) confirm that you remain an unpredictable and dangerous person, continuing to suffer from violent urges.
"I am fully satisfied that the seriousness of these offences is such as to justify the imposition of a sentence of imprisonment for life."
Whelan, a former Matalan worker, began using cannabis aged 16 and was said by a relative to have been in an "emotional and tearful" state on the night before the killings on February 25 this year.
The court heard on Friday how the younger victim's 22-year-old son, Liam Parker, took his own life in April after finding his mother's body.
The court was also told that a bloodstained axe was found near the body of Rose Hill, who lived in Sheffield but was visiting her daughter, having arrived in Shirebrook a couple of minutes after her grandson.
Post-mortem examinations found Rose had been strangled, while her daughter, who had wounds to her fingers and chin, had been punched in the face, knocking out one of her teeth, before she was drowned.
After the killings, Whelan was seen in Louth, Boston and King's Lynn before catching a train to London - where he was arrested two days later after ringing the police from a decorating store.
The churchgoer, said to have had a "fundamentalist" Christian upbringing, informed a call-handler: "I have done something really bad, a murder. It's my auntie and my nan. I have messed up, I need to serve the punishment."
Whelan, who appeared in the dock wearing a dark blue suit, is believed to have started using cannabis aged 16, smoking around an ounce of the drug each week.
Jailing the double-killer, Mrs Justice Carr accepted evidence that he had taken £100 and a bank cards from his aunt's purse after killing her, and had moved a dining room chair into the cellar before severing an artery in his grandmother's wrist.
"I am sure that you inflicted significant physical suffering on both of them," the judge told Whelan. "You also inflicted mental suffering, at least on Rose, with the use of an axe as a threat.
"These were savage and brutal attacks even before the killings."
Addressing the defendant's mental state, the judge added: "There is no suggestion that your ability to understand the nature of your own conduct was in any way impaired.
"You knew what you were doing and that it was wrong, even if your ability to form rational judgment or to resist you violent urges was mentally impaired.
"Your violent urges were exacerbated, as you knew, by your long-standing use of cannabis. Even if cannabis did not play any direct part in your offending at the time of the attacks, you smoking of cannabis was one of the triggers for the killings."
In his account of the run-up to the killings, Whelan said he had previously helped out with gardening at his aunt's home before a row over a spilt bucket of water led to a fall-out.
The court heard Whelan had suffered from anxiety throughout his life and developed obsessional thoughts from a young age of violence towards others - even fantasising about killing a stranger on a bus.
Speaking after the case, Whelan's father - who asked not be named, told reporters: "At the end of the day, for me it's the weed that's at the centre of all this.
"There's too blase an attitude. It's ridiculous."