A graduate with a fixation for serial killers and mass murder was planning "the perfect murder" when he bludgeoned and stabbed to death a mother and her teenage son.
Gregory Davis, 24, was detained indefinitely at a mental institution after Luton Crown Court heard how he armed himself with a carving knife and hammer and attacked three people.
Davis, of Milton Keynes, killed Dorothy Rogers, 48, and her 19-year-old son Michael at their home in Great Linford, Milton Keynes, on 28 January 2003.
On Monday he pleaded guilty to manslaughter on the grounds of diminished responsibility and to causing grievous bodily harm with intent to Michael Cowells, Mrs Rogers's boyfriend.
The court heard Davis was in the grip of a "psychotic episode" when he killed.
He was analysed by five psychiatrists who agreed he suffered depression, alcohol dependence and social anxiety.
Mr Justice Richard Aikens accepted the plea and said: "I'm satisfied you are suffering from mental illness and that it is appropriate that you be detained in a hospital for mental treatment."
Patrick Browne QC, prosecuting, said Davis knew Mr Cowells and Mrs Rogers from a the Pilgrim's Bottle pub, Great Linford, where they used to drink.
At the height of his depression he took a knife and hammer to Mrs Rogers's home on the Stantonbury Estate.
Serial killer 'ambitions'
After an argument in the house he attacked Mr Cowells with the hammer and then turned his attention to Mrs Rogers and her son.
Michael Rogers, who was killed after witnessing his mother's death, had tried to escape from the house but was stabbed in a nearby children's playground.
The court was told Davis's original idea had been to kill Mr Cowells.
Mr Browne said the defendant had "ambitions" to be a serial killer and was fascinated with mass murder and killers.
He read extracts from Davis's diary which detailed a formula for his future life.
It read: "Quit job tomorrow. Get Mick killed. Get Stuart to withdraw cash everyday. When all gone, kill him.
"Repeat Mick plan ad infinitum all over country and world in Las Vegas and swanky bars."
In mitigation, Graham Parkins QC said: "The general public must appreciate this was the action of a sick man."
Mr Cowells, 63, has since died after a fall at home.