A man who murdered a retired CPS lawyer planned to carry on killing vulnerable gay men as a progression from mutilating dozens of cats in Norwich, a court has heard.

David Iwo, 23, formerly of Palmer Road, Norwich, laughed as he was sentenced to a minimum of 33 years at Preston Crown Court on Wednesday for the murder of Martin Decker.

The 69-year-old was bludgeoned to death with a hammer at his home in Birkenhead, Wirral, on March 6.

Alan Kent QC, prosecuting, said the murder was part of a campaign of violent robberies of vulnerable men.

He said: "Had he not been caught he would have killed again and would not have stopped until he was caught."

The court heard Mr Decker, who worked for CPS Mersey Cheshire as a senior lawyer from 1986 until he retired in 2012, had contacted Iwo in March after seeing his advert offering sexual services on an app.

Iwo, who appeared via video-link from HMP Manchester, later told police he arranged to go to Mr Decker's home and they had agreed he would be paid £250.

He armed himself with a hammer and travelled from Liverpool to Wirral with the intention of murdering Mr Decker, the court heard.

In a police interview, Iwo said he had shaken hands with Mr Decker, who offered to get him a drink, and when he turned his back to him Iwo had struck him with the hammer repeatedly.

The court heard that Mr Decker had suffered a “determined and targeted attack” with an estimated nine hammer blows causing multiple skull fractures and that would have died quickly from his injuries.

Iwo then searched his victim's clothing and home and took cash, alcohol and valuable electrical items from his house.

He was arrested at a hotel in London on March 10. Police later recovered a blood stained claw hammer hidden at a property he had stayed at Dartford in Kent that contained both his and Mr Decker’s DNA.

Iwo told police he didn't view Mr Decker as a human but as "an objective", and saw the murder of a human as a "progression of his habit of killing cats", Mr Kent said.

He also said he had attempted to strangle a man the week before.

Mr Justice Jacobs said: "You attacked gay men, confident they were not going to report an attack."

In a letter to a psychiatrist, Iwo said he enjoyed a life "operating outside of the law".

He said he had enjoyed watching cats struggle and described various ways he had tortured and killed the animals, becoming known as the "NR3 cat killer".

“I used to enjoy watching the owners' efforts on Facebook and in community posters as they attempted to find their lost cats. I knew they were dead,” he added.

The court heard that Iwo told police and psychiatrists he had made a conscious decision to live his life by killing and stealing from people who approached him for sex and he would go on until he got caught.

A psychiatric report found he had dissocial personality disorder and was highly narcissistic, with little or no capacity to experience guilt or remorse.

Iwo, who had pleaded guilty to the murder at a hearing in September, refused to have legal representation during the sentencing.

When asked if he wanted to make any points Iwo, who was smiling as some of the facts of the case were outlined, said: "I've got nothing to say."

In a statement read to the court, Mr Decker's brother, Jeremy, who discovered his body the day after his death, said: "Martin deserved so much better. He was a lovely man who was taken from us all."

He said their 88-year-old mother relied on him and he doubted she would ever recover from the loss.

Detective chief inspector Rachel Wilson of Merseyside police, said: “This was a brutal and senseless killing of an elderly man in his own home which has obviously devastated his family and wide circle of friends and shocked the whole community.”

The cat attacks in Norwich involved one called Bubba, who had both its ears cut off and was slashed down its back.