Matthew Shaun McGrail, 25, was arrested the morning of the allegations and consented to officers taking swabs from his body.

In a video of the forensic procedure played at his trial on Thursday, McGrail appeared with paper bags over his hands and no shirt.

He is heard telling officers he consented to "everything".

"I will do absolutely everything to help you with your case," he said.

Officers took swabs from his hands, mouth and genitals.

He also asked, "so she's really said I raped her?"

In a later interview with police he denied anything had happened, saying "you just don't do that" to a friend's girlfriend.

Officers had arrested him about 5am, but a alcohol breath test reading of about 0.1 meant his interviews with police were delayed.

He said he was trying to not drink but when he did it was problematic.

A forensic medical officer who examined the girl in the hours after the alleged assault said there were red marks on her body consistent with rubbing or suction, but it was difficult to say when they were received.

A 2mm red abrasion near the girl's genitals was "fresh", showed no signs of healing and was probably a recent injury, the doctor said.

Under cross-examination by defence barrister Richard Thomas, she agreed the abrasion could have happened in the last day.

The girl had been at McGrail's flat in the early hours of January 24, 2015 with her boyfriend, when her boyfriend left to get a cigarette. It's alleged that when McGrail returned and they were alone in the flat the offences happened.

The court has previously heard that her boyfriend returned to the flat shortly after the alleged offences and the couple fought. Police said they found the pair that morning fighting in Garema Place.

McGrail faces trial on five charges, including two counts of sexual intercourse with a young person under 16, two indecent acts and one of attempted sexual intercourse.

The trial continues before Justice John Burns.