ONE of Australia's most dangerous sexual offenders has had his sentence review postponed after fresh allegations he sexually assaulted a fellow prisoner.

Corrective services has submitted material alleging Raymond Henry Garland sexually assaulted a prisoner at the Blackall watchhouse in August.

The Mackay rapist's defence barrister Marshall Cook said on Wednesday in the Brisbane District Court they had not had time to go through the documents thoroughly.

Mr Cook said police had been involved for some time and had indicated investigations could take a further two months.

Crown prosecutor Sarah Farnden explained police commitments to the G20 Summit in Brisbane had hampered their investigations.

She said now the summit was over, investigations were progressing.

Judge Kerry O'Brien adjourned the matter to February 13.

Garland, who admitted to having rape fantasies several times a week, has been subject to sex offence allegations while he was in the general prison population as recently as 2011 but no charges were laid.

The sexual predator who committed sex attacks in Mackay and Brisbane had an appeal rejected in February of this year.

Garland raped and sodomised a 14-year-old girl in 1985, sodomised two teenage boys in 1987 and held a group of people hostage in South Mackay in 1997.

He raped a five-months pregnant woman and sodomised a 16-year-old boy during the nine-hour siege.

He is serving four indefinite jail terms and was refused a fixed sentence, or a life sentence, when his case was reviewed in 2012.

- APN NEWSDESK