Convicted triple murderer Max Sica will learn on Friday if he has also been found guilty of child sex offences.

Sica's trial over allegations he had sex with a young girl about 100 times finished late last month in the Brisbane District Court.

Sica, 42, pleaded not guilty to 21 charges including maintaining a sexual relationship with a child, rape, carnal knowledge and indecent dealing between November 2004 and September 2008.

Judge Michael Shanahan, who reserved his decision, will deliver his verdict on Friday morning.

Judge Shanahan was tasked with deciding on Sica's guilt after Sica won the right to a trial without a jury.

Sica's lawyers requested this uncommon form of trial because of fears a jury might be unfairly influenced by the publicity of their client's murder case.

Sica is already serving 35 years in jail after being convicted last year of the murders of his ex-girlfriend Neelma Singh, 24, and her siblings Kunal Singh, 18, and Sidhi Singh, 12, in 2003.