While testifying, Marc Hamilton was asked by prosecutor Anthony Stephen to page through a file of photographs taken at the scene.
Presiding Judge Nathan Erasmus warned him: "The photos are gruesome, so prepare yourself for a shock."
Hamilton said he arrived at Sizzlers at 03:14 on January 20 last year and the first thing he noticed was the security gate was open.
As he entered the premises he saw four bodies on the floor in a room.
He told the court: "It did not register with me what had happened, and I continued to walk down a passage."
In a massage room he saw a second body, tied up, with a huge pool of blood around the head.
It was only then that he realised something had gone badly wrong, and he ran from the house to a nearby petrol station where a police patrol van had just arrived.
'I don't want to die!'
He told the court: "I told a policeman in the vehicle he must go immediately to the house in question, but he said he could not. At the petrol station I saw a man on his knees screaming, 'I don't want to die'.
"The second time I told the policeman to accompany me to the house, he did so."
The screaming man was apparently the only person to survive the killings. He is scheduled as a State witness in the trial.
Hamilton said he went back into Sizzlers with the policeman and in a room they found four boys, one of them choking with a gag in his mouth.
Hamilton said the gag was removed and the cord used to tie the boy up was cut.
Hamilton said he then heard further choking behind him and he and the policeman then found another person on the floor behind a bed.
After they found a fifth body, paramedics arrived and Hamilton was told to leave the house.
Hamilton said each body had its hands tied behind the back, the feet tied together and the hands then tied to the feet.
Before the court are Waterfront restaurant waiter Adam Woest, and his taxi operator friend Trevor Theys. The judge has entered a plea of not guilty for them on nine counts of murder, one of attempted murder, one involving the theft of two firearms, and armed robbery.
Also on Thursday, the court heard that a courting couple in a car parked near Sizzlers heard several gunshots in the early hours before seeing two men running from the male massage parlour to a nearby BMW.
State witness Darren Brick said the two men were dressed in black and wore masks.
He said they ran in a "calculated, meticulous manner, as if it had been planned, like you see in the movies".
Brick told the court one of the two men headed for the driver's seat of the getaway BMW as they fled the massacre scene, and the other ran to the front passenger seat, "like they came to do something, did it, and were now leaving".
He told the court his fiancee immediately reported what they had seen by dialling an emergency number on her cellphone, and they (Brick and his fiance) then drove towards Beach Road.
He told the court: "We were followed by the BMW, with its headlights off, and at the Beach Road T-junction the BMW turned right while we turned left."
Brick said he reported what they had seen to staff at a nearby petrol station, as well as to the Sea Point police.
A second State witness, Jacobus Adriaan Steyn, who lives in the Bordeaux apartment complex near Sizzlers, told the court he and his partner were awoken about 03:20 by five to seven gun shots.
He said his flat overlooks Sizzlers, and through a window of his flat, he noticed lights on at Sizzlers.
He told the court he knew something had happened when he saw two men running from Sizzlers "in a clumsy fashion, carrying weapons.
"I realised people had been shot," he told the court.
He said he often heard the Sizzlers steel security gates "clang shut" as people came and left through the night but he did not hear the gates slam shut this time, which he thought rather odd.
He told the court it was a "moving experience" to afterwards see bereaved people place flowers on the gate and fence at Sizzlers.
"It was their way of communicating with the dead," he told the court.
He said people lit candles on either side of the gate, and a woman regularly sprayed flowers on the gate and fence to keep them fresh for as long as possible.
He said Woest lived in the same block of flats as himself, and they often shared a lift.
The case continues on Monday.