FOUR international students were subjected to a "reign of terror" by a depraved homeless man who held them hostage and raped two of them repeatedly at knife point, a court has heard.

Brendan Dennison, 27, pleaded guilty last December to 19 charges including the murder of a young Asian woman and causing grievous bodily harm to her boyfriend after the naked couple fell from the balcony of their Waterloo apartment trying to escape the hour-long ordeal.

Dennison also admitted ordering the couple to perform degrading sex acts at knife-point and robbing and threatening another two young women in the flat with rape.

His lawyer, John Stratton, SC, told a sentencing hearing in the Supreme Court his client had been injecting the drug ice for a week prior to the attack and had no memory of it.

Mr Stratton said Dennison was "wandering homeless and aimless" and hadn't slept for at least two days.

The court heard he followed a friend of the couple's into their Hunter St building through a security gate and then held a knife to her throat in a lift in what was intended to be a robbery.

Mr Stratton said the initial crime was "opportunistic" and escalated when Dennison found himself in an apartment with a male and three young women.

Justice Elizabeth Fullerton said he subjected his victims to "what can only be described as a reign of terror."

But Mr Stratton said the sexual nature of Dennison's attack on the couple, particularly on the male, was "completely out of character" and could possibly be explained by the drug as "it is known to increase sexual desire."

Psychiatric evidence tendered to the hearing stated Dennison was "borderline mentally retarded" and Mr Stratton said he did not take the stand as he felt he couldn't express himself clearly.

Instead, he tendered a hand-written letter to the judge, which was not read to the court, allegedly speaking of his remorse.

He will be sentenced on June 4.