Unusually, Dara Florence proved to be a crucial eyewitness at the heart of arguments for both the prosecution and the defence.
She was the only one in the house who had not been drinking that night. The young Belfast woman opened the door during the alleged incident and observed the scene before her for "less than a minute".
She told the court that she had seen what she termed a "threesome" and saw no sign of distress on the part of the young woman. Coming up the stairs, she heard moaning which she later told police in her second statement she had not t hought was sexual, though later she said that what she had heard was sex.
She was "100%" positive she had witnessed Paddy Jackson having penetrative sex with the alleged victim, despite his denial.
Brendan Kelly, QC for Mr Jackson, put it to her that she had "assumed" this from "the movement" but she told him: "It was 100%; I saw sex, from the movement."
In his closing statement, Mr Kelly QC described her evidence as "extraordinary".
"Dara Florence confirmed from what she could see (the woman) was not distressed," he said.
"When people commit crime they tend to hide, they tend to conceal what they did because they don't want to get caught," he said. "What did these two violent rapists do when she walked in? They invited her to join in. Dara Florence is absolutely central to this case."
For Toby Hedworth QC for the prosecution, Ms Florence was also a crucial witness - and he focused on the fact that she had seen penetrative sex. In closing, he told the jury she was "certainly not expecting to walk in on non-consensual activity".
He asked Ms Florence if she had seen any signs that the woman had positively consented that night and she replied that she had not.