When a girl refused to have sex with him, Gang Kaewklom said "I'll show you what angry is", hit her in the face three times, dragged her on the ground in a Sydney car park and kicked and stomped on her head.

The 15-year-old girl, who cannot be named, made a triple-0 call during the attack, which picked up what Kaewklom was saying to her.

"I love you so much you f---ing lucky bitch, f---ing slut. Get up," he was recorded as saying.

Five days later, when he was waiting in a cell for the ensuing assault case to be heard in Liverpool Local Court, Kaewklom launched a similar attack on 69-year-old prisoner Frank McGregor, throwing him to the ground and stomping on his head with both feet.

Kaewklom, 20, pleaded guilty to the murder of Mr McGregor, after initially trying to argue he was guilty of manslaughter because of a "substantial impairment", and also admitted the attack on the girl.