A man accused of strangling his girlfriend and killing her two siblings has allegedly "confessed" to killing her to a friend, who was writing a book on the murders, a court heard.

Prosecutor Michael Byrne told the Brisbane Supreme Court that even without the confession, the Crown had a circumstantial case to convict Max Sica of murdering Neelma Singh, 24, Kunal Singh, 18, and Sidhi Singh, 12 at their family home at Bridgeman Downs in Brisbane.

Their dead bodies were found in a spa bath on April 21, 2003,The Courier Mail reports.

Byrne said the Crown alleged a confession by Sica to a friend Andrea Bowman would be an extra layer of comfort in the jury's decision.

He said Bowman, who had known Sica since the 1980s, contacted her when he featured on television reports about the killings.

Byrne said Bowman asked Sica if he was remorseful and Sica said that he cried for what he had done and wished he if could take his act back.

He said Sica had regularly accused Bowman of speaking with police and he must have had at least some idea his comments would be reported to the authorities.

He added that Sica had lied to the police about his relationship with Neelma saying it was "all good, no arguments.

Sica continued to deny he had been at the Singh house on the night of the killings but at a late stage admitted he was supposed to be there only when confronted with evidence of text messages.