The Sydney man, now 22, was playing online game League of Legends with his friend, a high school student boarding at the Magregor home of Paula Conlon, 30.

killed in a room just metres away from the student.

Her then boyfriend, Aleksander Vojneski, 31, has been accused of stabbing her to death, and is on trial in the ACT Supreme Court.

The Sydney-based gamer gave evidence on Thursday of what he could hear through his computer speakers that night.

He said he thought he started a game of League of Legends about midnight or later, and about 22 minutes in he heard arguing coming through his friend’s microphone.

The witness said he could hear voices of a woman and a man, although the man’s voice was harder to hear.

He said there was then a period of "dead quiet".

"Then maybe after a few more minutes of silence I heard a really loud scream," he said.

He said he asked his friend what was going on in the house.

Under cross-examination by defence barrister Jack Pappas, he agreed his friend had said he hadn’t heard anything.

A third young man, who went to school with the boarder, also gave evidence on Thursday afternoon.

On the night of the murder, he said he’d been at his home and was eating dinner, before going back to his computer and using a voice chat application, TeamSpeak 3, which the other two gamers were using to talk while playing League of Legends.

He said they were talking about something that had just happened.

The witness initially told Crown prosecutor Shane Drumgold that Ms Conlon’s boarder had spoken of hearing a scream.

He saw the boarder the next day on the school bus, and said he must have been mistaken about when his friend has spoken of the scream.

Earlier on Thursday, a police fingerprint expert gave evidence about finding Vojneski’s prints in the house.

It is alleged that knife is from the same set as the one used to kill Ms Conlon. The actual murder weapon was never found.

The trial continues before Justice John Burns on Friday.