British media report he was last seen in 1997. It's believed the couple moved to Beddau, a quiet village near Pontypridd, in February that year.
Three weeks after his wife's death, Mr Sabine's body was found, reportedly by neighbours, in the garden of the block of flats where they lived. The body was lying above the ground, wrapped in plastic.
BBC Wales reported today that DNA analysis confirmed Mr Sabine's identity and his injuries were consistent with assault.
No missing person report was ever filed for him and police are probing the death and the apparent concealing of his body.
Officers are also investigating the couple's financial activity.
They had estranged children, who have been located and informed, BBC Wales said.
Locals told the BBC the pair were originally from New Zealand and it's possible their children remained here.
In a 2012 magazine interview about her garden, Mrs Sabine said she had "grown up with dirt" in New Zealand.
A neighbour, Violet Scott, 75, told the Daily Mail online she couldn't believe a body had been there for so long.
"Leigh was a very talkative and outgoing woman but it is hard to comprehend what has happened," she said.
"I didn't know her husband but I know he was a fireman and we all thought he died a dozen or so years ago.
"It could be that she kept his body in her home and then decided to move it when she knew her own end was close."
Ms Scott was struggling to comprehend that Mrs Sabine could have been a killer.
"Leigh could be very straightforward but it is difficult to think she could have killed someone. She had another man living there for a few years but he left -- I don't know what happened to him.
"I asked Leigh if she would ever go back to New Zealand. But she told me, 'No -- I could never leave here'," she told the Daily Mail Online.
Another local, who asked not to be named, told Mail Online nobody could believe the police announcement.
"We all knew her. She would come in here and even used to bring us presents at Christmas. We called her 'mad Leigh' because she had her funny ways," the local, a hairdresser, said.
"She had a heart of gold, though. She is the last person you would expect to be accused of something like this."
Police have launched a public appeal for information.
"This is an extraordinary set of circumstances and we are working tirelessly to put together the pieces of what is a complex investigation," South Wales Police Detective Chief Inspector Gareth Morgan said.
"We would appreciate hearing from anyone who knew John and Leigh Ann Sabine and who may have socialised with them or met them back in 1996-1997.
