Rappel had been on trial in the ACT Supreme Court, with several other men, over the attack that left one of the victims requiring hospital treatment for a collapsed lung.

All five accused - Rappel, 43, Alex Bourne, 30, Daniel Grech, 28, Jeremy Leigh Jackson Reid, 26, and Isileli Paea Taholo, 31 – had pleaded not guilty to two counts each of intentionally inflicting grievous bodily harm.

However, mid-trial, Rappel switched his plea to guilty to the charges. The charge of intentionally inflicting grievous bodily harm carries a maximum sentence of 20 years jail.

Grech also pleaded guilty to a count of common assault.

Justice Michael Elkaim declared the hearing of Mr Bourne, Mr Reid, and Mr Taholo a mis-trial, and the charges will be revisited after Rappel and Grech are sentenced on Thursday.

The court on Monday heard the brothers had been bashed in their cells at the Alexander Maconochie Centre on August 7 last year.

As a result, the younger brother was hospitalised with 36 individual injuries, including a collapsed lung and fractured ribs and facial bones.

The elder was also taken to hospital so a tear injury to his ear could be stitched up.

Footage of the incident, captured on the jail’s CCTV system and played in court on Monday, did not show exactly how the brothers suffered the injuries as cameras are not located within the cells.

However, the footage shows a number of men go into a cell occupied by the younger of the alleged victims, before the men then go upstairs into his brother’s cell.

The older brother – who appears to be bleeding from his ear – then goes downstairs into his sibling’s cell.

The group follows and two punches are thrown at the doorway, before the men disappear out of sight into the cell.

The brothers said they did not know who attacked them when they were called to give evidence on Monday.

The matter will return to court for sentence on Thursday.