Paul Lavern Ritch, 37, from Roath, Cardiff, was stabbed early on Sunday morning after a night out with friends in the town of Margate, New Jersey.

It is thought Mr Ritch may have stepped in when he saw someone being attacked.

The 37-year-old was well known in Cardiff through sporting activities and worked at the city's David Lloyd club.

Mr Ritch - known as Lavern - was once short listed for Company magazine's bachelor of the year and also included in the Wales on Sunday newspaper list of eligible bachelors.

It is believed he had been visiting a friend from nearby Cherry Hill and spent Saturday night at restaurants and clubs in Margate, a fairly affluent resort on an island a few miles from Atlantic City.

The sportsman, who also worked as a swimming and tennis coach, was declared dead an hour after being taken to hospital. A major crime unit is now investigating.

It is the first murder in the seaside resort for more than six years.

Police issued a sketch of the suspect on Tuesday

Thomas Hiltner, Margate's municipal clerk, said he believed Mr Ritch had been leaving a pub and may have seen somebody chasing another person.

"My understanding is he was trying to maybe aid or help, maybe fend off, or help distract the perpetrator, maybe try and help out the guy that was being chased obviously wrong place at the wrong time because the perpetrator was carrying a knife," he said.

Police are searching for the murder weapon while the Atlantic County medical examiner's office has confirmed Mr Ritch died from a single stab wound to the heart.

Phaedra Laird, a reporter with Channel 40 TV news, said the fact the Atlantic County prosecutor had held a rare news conference spoke volumes about how hard they are trying to solve the crime.

They had released photographs from surveillance footage featuring a man they want to speak to and had appealed to the public to identify him.

He was a very peaceful guy who was always stepping in and helping people, that's the type of person he was. He was just perfect, he was lovely and it's just a tragedy

David Knibbs, friend

She said the man police want to speak to had been ejected from a bar at 0100 local time.

She had unofficially been told the man may have returned to the bar looking to pick a fight - an event unconnected to Mr Ritch and his friends.

"What I'm gathering is maybe that fight between those two separate people ensued on the street, a chase took place and sensing that something was wrong, Lavern Ritch chased after them.

Friends of Mr Ritch have said it would be typical of him to step in if he saw someone in trouble.

Fellow swimming instructor David Knibbs said: "He was a very peaceful guy who was always stepping in and helping people, that's the type of person he was. He was just perfect, he was lovely and it's just a tragedy."

David Lloyd health club in Cardiff, where Mr Ritch worked, planned opening a book of condolence.

In 1998, Mr Ritch took part in the ITV programme Gladiators.

His family are being comforted by relatives at their home in Fairwater, Cardiff.