A court heard accused killers played video games and drank while two people were bound and bleeding metres away, and that later they sat on the lid of a toolbox to keep the two now-deceased people inside.
A fourth man, Waylon Walker, is accused of their murder only.
Mr Harrington was inside the Kingston unit where police allege the four accused, playing varying roles, ultimately lured Breton and Triscaru to their deaths.
Over the course of several hours on January 24, 2016, Harrington said the accused bound the pair’s ankles and hands with zip ties, questioned them and beat them, before forcing them into the toolbox.
The court heard the accused sat on the toolbox to keep the lid shut, even playing video games and drinking.
Harrington told the court it was Daniels who was calling the shots.
He wanted to scare them because he suspected drug dealer Breton was “a rat”.
“A police informant?” the prosecution asked.
“Yep,” Harrington replied.
He said at one stage, when the others had left the room, he spotted Triscaru trying to escape.
She put her fingers to her mouth to silence him, but he alerted the others who put her back in the toolbox.
Under cross examination, the effects of Harrington’s alcohol and drug abuse on his memory was raised.
He admitted once he went six days without sleeping on an ice-fuelled bender.
All the accused have pleaded not guilty. The trial continues tomorrow.