A "dangerous" knife-wielding man who was seen fleeing the scene of a fatal attack on an 87-year-old Irish man in a mobility scooter is being sought by detectives in west London.

Thomas O'Halloran was killed in a "shocking act" of "unprovoked violence" at around 4pm yesterday, the Metropolitan Police said.

Mr O'Halloran was originally from Ennistymon in Co Clare and lived in the Greenford area of west London.

He is survived by his brothers George and Richard, and sister Bridget, as well as many nieces and nephews, who live locally in the west Clare town.

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Officers were called to Cayton Road in Greenford yesterday afternoon to reports of a stabbing and the charity fundraiser was declared dead at the scene.

Detectives have released images of a man they say they want to identify as "a matter of urgency".

He was armed with a knife and wearing grey shorts, a dark T-shirt, a white baseball cap and white patterned builder-style gloves.

Police released this image of a man seen leaving the scene

Detective Chief Inspector Jim Eastwood, who is leading the investigation, said: "He is clearly a dangerous individual and people are advised not to approach him, but to call us immediately on 999 if they know him or have any information regarding his whereabouts."

Mr O'Halloran was killed in a "shocking act" of "unprovoked violence", Metropolitan Police Chief Superintendent Sean Wilson said at the scene.

Mr Wilson said: "I understand that our community will quite rightly be shocked and appalled by this incident, as I am too.

"We are now able to name the man who has tragically lost his life as Mr Thomas O'Halloran, who lived in Greenford and was a very well-known and much-loved member of our community."

He was attacked while on his way to busk, according to a friend, who did not want to be named.

He told the PA news agency: "He was coming back from Perivale to play his accordion and make some money for his family and he was stabbed to death."

Forensic officers at the scene near to Cayton Road, Greenford, in west London

Mr O'Halloran was said to be known locally for busking outside Greenford Station and was also said to be raising money for war-torn Ukraine.

A man who works in a newsagents outside the station said: "He used to play his accordion here.

"He came every day for a long time, at least two years. He usually busked around five o'clock."

Another shopkeeper said: "He was often outside the station playing his accordion."

Frasley Coutinho, who lives in Greenford, west London, opposite where the attack happened, said he saw the victim surrounded by a group of young boys.

He said: "I saw a couple of people gathering around him and then he drove past and stopped further up, and then there was a group of young boys around him."

Tributes to native of Ennistymon

Clare Fianna Fáil councillor Shane Talty said Mr O'Halloran was "a native of Ennistymon and kept in contact with his wide circle of relatives in Ennistymon, who are well-known locally and respected.

"All the thoughts of the community are with the O'Halloran family at this time."

Fine Gael Senator Martin Conway said the community was in deep shock at Mr O'Halloran's death.

He said: "The news of the brutal murder of Thomas O'Halloran has shocked the people of Ennistymon and north Clare.

"It is almost unbelievable, that a man of his age using an electronic mobility device, was targeted and murdered in broad daylight. It is truly shocking.

"I sincerely hope the perpetrators are brought to justice as soon as possible," Senator Conway said.

"'Tommy' as he was known left Ennistymon for London 71 years ago but travelled home almost every year until about 10 years ago."