A man who admitted killing two unarmed female police officers fantasised about decapitating another of his victims, a court heard.
It was alleged Dale Cregan claimed to have enjoyed "the best sleep of my life" after shooting David Short three times in the head at point blank range and blasting his body to pieces with a grenade.
Preston Crown Court heard that Cregan, 29, feared members of the Short family would harm his family and he admitted killing Mr Short and his son Mark before murdering Pcs Nicola Hughes and Fiona Bone in September last year in a gun and grenade attack.
It was claimed that during three interviews with a forensic psychiatrist Cregan revealed that he struggled to suppress violent thoughts about the Shorts.
Dr James Collins said Cregan, who only has one eye, told him that David Short had threatened to rape his sister and his son and set him on fire.
Quoting from notes he made of the interviews while on remand at HMP Manchester, Cregan told the psychiatrist: "I couldn't get him out of my head. It was on my mind constantly, I could not put the thoughts away.
"I thought if I kill him, maybe I will get a rest. When I was having my fantasies I used to think about stabbing him repeatedly, smashing his head with a hammer and cutting his head off.
"I shot David Short point-blank in the head, three times, but I would have preferred it if I would've used a knife. I felt calm before killing David Short but, after, a big relief rushed through my body.
"If I'd had time, I would have cut his head off and arms and legs. I would've gone and got a knife from the kitchen and used that.
"The thoughts were such, I knew I would have to do it. However, after I killed Mark Short, he said he would rape my son, he said he would set him on fire.
"He threatened my whole family. He told me 'The gloves are off'. So I was always going to kill him. It was not an urge - it was because what it was doing to me if I didn't do it."
Cregan denies the murder of David Short at his house in Clayton, east Manchester, just months after shooting dead his son Mark Short in an attack on the Cotton Tree Pub in Droylsden, Manchester, on May 25 last year. He also denies four counts of attempted murder and causing explosions.
He admitted luring Pc Hughes, 23, and Pc Bone, 32, to an address in Mottram with a bogus burglary report before opening fire on the officers and throwing a hand grenade at the two women as they lay dying.
Under cross examination by prosecutor Nicholas Clarke QC, Dr Collins said Cregan claimed to have been thinking of killing David Short for five years "in a general sense" but that his fantasies had become more specific in the weeks leading up to his murder.
He also admitted firing a gun loaded with blanks five times at his enemy although denied involvement in an incident when David Short was knocked off his motorbike and had his throat cut, it was claimed.
The psychiatrist said Cregan denied the dispute with the Shorts was over drugs even though he was a cocaine dealer who was making £20,000 a week by importing the substance from Holland.
He said the dispute with the family dated back to childhood when nephews of the Shorts would come to his neighbourhood and have fist fights with him. The court heard that he refused to be bullied and it was at that point that he developed a "bad fetish" for knives, the jury was told.
Cregan built up a collection of 10 firearms including machine guns and bought grenades from Holland, it was claimed. He acquired the weapons not to protect himself whilst dealing drugs but because he was interested in them, he told Dr Collins.
It was alleged he told the psychiatrist: " I was also worried about my mother and brother. Since I lost my eye it's been worse."
"I thought if I killed David Short I thought all these thoughts would go away. I did feel better after killing him. I felt better for a couple of days but all the thoughts came back. The paranoia was so bad I used to just sit in the house on my own.
"David Short was the biggest threat. I felt quite good about myself when I killed him'," he added.
The trial continues. All defendants deny the charges against them.