Quinton Taylor, the only survivor of the massacre, recognised Theys on a photo in a police album soon after he was released from hospital after the killings.
The photo of Theys was taken 12 years ago when he was involved in a vehicle theft case of a relative. The case was dropped but the photo was never destroyed.
As a result Theys was arrested a month after the massacre. His testimony led police to Adam Roy Woest, the co-accused.
Theys and Woest were found guilty of murder last week.
Taylor, whose throat was cut and who had two bullet wounds to the head, was left for dead.
When he regained consciousness, he walked through the rooms of the massage parlour where he saw the tied, bloodied bodies of Aubrey "Eric" Otgaar, Warren Visser, Stephanus Fouche, 17, Sergio de Castro, 22, Marius Meyer, 21 and Travis Reade, 20.
He spent two weeks in Groote Schuur hospital, where he was first treated for the wound to his neck. He stayed at his parent's home in Muizenberg for a while, before returning to hospital to have the bullets removed from his head.
Tayler said Inspector Jonathan Morris, the investigating officer, often visited him at home. On one occasion, he showed Taylor a file with photos of criminals.
And then the miracle happened. "I identified Trevor Bazil Theys on an old photo as the man who cut my throat and shot me in the head."
This put the police on Theys's trail, and he revealed everything after his arrest.
The police set a trap for Woest at the Waterfront restaurant where he was working.
Taylor was put in a witness protection programme.
"I spent more than a year in the programme," Taylor said.
"I hated it because I was cut off from my family and friends. I wanted to tell the world what had happened in the early morning hours of January 20, but I couldn't. I nearly went crazy without psychological counselling.
"Counselling was organised for me just before I testified in the Cape High Court on Monday, on my birthday, when I looked the two accused in the eye for the second time."
Taylor summed up the Sizzlers massacre as follows: "Eric and Godfrey tried to fight back, and they died. I accepted that I would also die.
"I was lying on my back and looked Theys in the eyes while he slit my throat. I don't know how I regained consciousness.
"I know God is a factor and I believe He gave me a second chance. A second chance to appreciate life more and to put more positive things back into it."