The police officer, who cannot be named for legal reasons, was cross-examined by de Belin's barrister, David Campbell SC, on Tuesday in Wollongong's District Court about witness statements that differed from the complainant's.

When the teenager initially accused the key St George Illawarra player and his friend Callan Sinclair of raping her in a Wollongong unit in December 2018, she never mentioned to police that another man was present in the apartment.

De Belin, 29, and his 23-year-old friend have pleaded not guilty to the aggravated sexual assault of a 19-year-old woman after meeting her in a bar nearby.

Two witnesses who made police statements around the time of the alleged assault said the woman had mentioned seeing another male in the vicinity.

But the lead investigator who took the complainant's statement never questioned her about this discrepancy.

"You couldn't get something more central.... at the very place she says she is sexually assaulted, another person turns up... didn't you consider this of central import?" Mr Campbell asked the police officer.

But the detective said he believed the issue was covered adequately in a police statement by the third man who was seen in the apartment.

Troy Martin had earlier told the court of seeing the accused duo standing with a naked woman on the bed in the bedroom.

Mr Martin initially lied when he told police that sometime during the night he heard sounds which seemed to come from outside before he went back to sleep.

Mr Campbell said it was "unthinkable for an officer in charge of the investigation" to not speak with the complainant following this revelation nor seek further clarification from Mr Martin.

Constable Benjamin Sutton assisting the officer in charge was also grilled about the lack of detailed notes taken throughout the investigation, as well as immediately following the initial complaint.

"Our priority was to get her to a hospital....the retention of that physical evidence was a priority at that time," Const Sutton said.

The officer could not recall making notes regarding many of his interactions with the young woman.

He also admitted serving a brief of "plainly privileged" material to the director of prosecutions.

"That should not have happened?" Mr Campbell asked, to which he responded: "In hindsight, no".

The detectives had intercepted and monitored both accuseds' phones for about two months following the allegations.

This resulted in more than 400 calls and 2000 messages from de Belin being monitored and reviewed, while Sinclair had a similar "vast amount" of mobile data retained.

It included a text message from de Delin about Mr Martin being home at the time the sexual activity took place.

"Broke into your house... Troy was there... haha whoops," the message read.

Despite three sources of information detailing another man being home during the incident, the "general of the troops" didn't question the woman about this, Mr Campbell said.

The trial continues.

Australian Associated Press