On the murder charges, restaurant manager Adam Roy Woest, and taxi operator Trevor Basil Theys face nine prescribed life sentences.
Judge Nathan Erasmus described the slayings as the "worst massacre that Cape Town and the country has ever seen".
He said the entire country had expected to hear during the trial why this had happened.
However, because the two killers elected to remain silent, this was not to be and "we are still left with more questions than answers".
The judge agreed with prosecutor Anthony Stephen that the robbery at Sizzlers had been premeditated, and that the massacre that followed had been preconceived.
He said when Woest and Theys entered the Sizzlers gay massage parlour in Sea Point in the early hours of January 20 last year, they had evil and criminal intent, and had no intention at all of innocently utilising the services of the parlour.
Although Woest and Theys had taken balaclavas with them to the scene, they had not used them once inside the premises.
The judge presumed this was because they knew there would be no survivors.
He said the court knew that they slit the throats of their victims. They had also gone to the scene with a container of petrol, presumably to torture their victims.
He said the court could not understand, and it was not explained, why Woest and Theys did not leave the massage parlour after the robbery, nor why the whole episode took three hours.
The reason for the massacre remained a mystery, he said.
The case was postponed to Monday for mitigation by the defence team.