Westport man Charles Jones, 56 - the president of the World Croquet Association - was found dead in his rented apartment in Pattaya, a popular holiday resort about 165km southeast of Bangkok.
His computer and cellphone had been stolen. Family said he refused to give thieves the combination for the apartment safe.
His sister Alison McMillan said CCTV footage showed a man entering her brother's apartment and leaving with his computer about half an hour later.
Neighbours heard sounds of violence, but did not go to check the apartment, she said.
"Some of the neighbours thought there was a boxing fight going on. But they didn't go in - they don't do that.
"It is very frustrating."
Ms McMillan said she had been told the man in the CCTV footage was a Syrian restaurant worker.
However, she had been frustrated by a lack of further information from Thai police.
She said her brother was a trusting man who would not hesitate to be generous - even to strangers - and may have given out information about himself on the night he was killed.
He had an injured shoulder and would not have been able to fight back when attacked, she said.
"Charles was just that kind of person. He would never see much wrong with people. He would never hurt a hair on anyone's head. He would fight with this mouth.
"There's no way he could ever fight off an attacker. He would give them a tongue lashing. If there were sounds of a struggle - it must have been awful."
The family's priority now was getting Mr Jones' body back from Thai authorities so a funeral could be held in New Zealand, Ms McMillan said.
"I never thought this would happen to Charles but it has. I thought we would be blathering on with each other for years. It will never be the same again."
Tributes for Mr Jones have come in from around the world.
Long-time friend Paul Archer said the death was "an absolute tragedy".
"I'm reeling from the shock of it. It's been a brutal brutal death
"He's world president of croquet, he's a JP, he's a QSM. He's hugely involved in the Westport community as he was in the Wellington communityHe was selfless with his time."
Mr Jones, a late convert to Catholicism, played the organ in Westport's St Canice's Church and was a volunteer helper at the O'Conor Memorial Rest Home. He returned to Westport about five years ago to look after his ailing mother, Jean, who died last year.
"When his mother was dying, for 22 days he laid by her side. He wouldn't leave her," Mr Archer said.
Buller Mayor Pat McManus, who heads the O'Conor Home Trust, said Mr Jones' death was "a real shock reverberating all around the Home".
"He was the type of guy everybody loved."
Mr Jones' contribution to the community, and his achievements in world croquet, were huge, Mr McManus said.
O'Conor Home spokeswoman Reece Durrant said Mr Jones was a "wonderful" man.
"He had a huge influence in all of our lives up here."
