A lawyer for convicted triple murderer Max Sica says it's impossible to prove beyond reasonable doubt that his client had a sexual relationship with a child.

Sica, 42, has been accused of having sex with a girl about 100 times in the four years to 2008, starting when she was nine.

Sica has pleaded not guilty to 21 charges including maintaining a sexual relationship with a child, rape, carnal knowledge and indecent dealing.

Because Sica is facing a judge-only trial, the media can report that Sica was convicted last year of murdering his ex-girlfriend Neelma Singh, 24, and her siblings Kunal Singh, 18, and Sidhi Singh, 12, in 2003.

Barrister Sam Di Carlo on Friday told the District Court in Brisbane there were too many things that didn't add up about the allegations against Sica.

In summing up his case, Di Carlo questioned why much of the sex allegedly occurred in open areas of his client's Brisbane house.

The home was occupied by a number of people, including Sica's wife and father, and there were regular visitors, Mr Di Carlo told the court.

He listed places where Sica allegedly had sex with the girl including the lounge room, kitchen, computer room and an upstairs bathroom.

He suggested his client would have used a spare room or the garage if the allegations were true.

"You couldn't have more open places," he told the court.

Mr Di Carlo also said a doctor who examined the girl when she was 13 found no evidence of trauma to her hymen.

And listening devices installed in several rooms in the house by police for a month in 2006 yielded no evidence, Mr Di Carlo continued.

"It beggars belief that in these circumstances that Massimo Sica would have sex in the kitchen, the lounge room, the dining room, all of these areas, and nothing comes out which would assist police," he said.

Sica was handed a 35-year sentence for the murders of the Singh siblings but he has lodged an appeal that will be heard after the child sex charges are resolved.

The trial continues.