A former Otago prisoner has admitted slitting the throat of a fellow inmate, using a razor blade fused to a piece of plastic.

The victim says he is "alive by a divine miracle".

Anthony John Wheble, 24, pleaded guilty to attempted murder when he appeared in the High Court at Dunedin last month but the facts of the bloody attack were only agreed recently.

It can now be revealed that the victim was 33-year-old Brazilian national Diego Marques-Santos.

He is serving a prison term of three and a-half years after targeting gay men through dating app Grindr, gaining their trust, drugging them and stealing from them.

His crime spree, divided between Nelson and Dunedin, yielded more than $10,000 in a matter of weeks.

He sent letters to the Otago Daily Times describing his hazy memories of the attack at the Otago Corrections Facility on October 20 last year.

"I remember some flashes of Wheble standing close, punching me," he wrote.

"I was saved by another prisoner who quickly blocked the bleeding by putting his top around my neck ... I was choking on my own blood."

He said that he had clashed with Wheble earlier and put in an official complaint about the man's behaviour with prison staff.

"Please help me. I don't want to die," he allegedly wrote.

But OCF director Dave Miller said a review of the incident showed there had been no previous complaints by the victim about the defendant.

Other allegations made by Marques-Santos had been referred to the police, he said.

On the morning of October 20, the prisoners in Wing H were released from their cells.

Wheble "stalked" his victim around the day room, court documents said, then grabbed him from behind, using his right hand to cut his throat.

The 8cm slice did not quite sever the carotid artery.

Marques-Santos lowered his head to protect himself while Wheble tried to cut him twice more with the implement.

Other inmates intervened but the ordeal was not over.

Wheble twice stomped on the victim's head as he lay in the recovery position.

After threatening other prisoners with the implement, the defendant again kicked the man's head at least five times "as if kicking a football".

Marques-Santos was airlifted to hospital, where he received 15 stitches to his neck as well as treatment for a nasal fracture and severe bruising.

He told the ODT Wheble had previously called him "terrorist scumbag" when they had shared adjoining cells.

The animosity continued when they were in a segregation unit together.

Marques-Santos claimed his assailant had been moved there because of a violent incident with another inmate.

Miller refused to address the point but confirmed both men were in voluntary segregation.

A review of the incident had resulted in changes to some Corrections protocol.

Staff now ensured that when a razor was returned after use, it was checked immediately to ensure it was complete.

Also, the names of all responding staff members were included in incident reports, Miller said.

In a wide-ranging rant, Marques-Santos' letter to the ODT took aim at the Prime Minister, the Brazilian consulate and the Canadian authorities for refusing him entry to the country three times.

He went before the Parole Board for the first time in November, where release was refused because there were no details of what awaited him in Brazil.

Marques-Santos will appear again this month and will be deported when the board decides.

Wheble was transferred to a North Island prison after the throat slashing.

He will be sentenced in the High Court at Auckland next month.