Kiwi Armstrong Renata allegedly causing trouble in numerous prisons in Australia

Since being in jail, Armstrong Renata has been involved in a number of altercations with prison guards. Photo / Supplied

Armstrong Renata, the New Zealander jailed for coward punching Cole Miller, will spend an extra three months in prison after pleading guilty to assaulting a guard.

In October, the 24-year-old was sentenced to seven years in jail for killing Miller, 18, while he was out with friends in Brisbane's Fortitude Valley.

Miller was celebrating Schoolies in January 2016 when he was hit in the back of the head by Renata.

The punch from Renata knocked Cole Miller out cold, causing his head to hit the pavement and the promising water polo player died in hospital two days later. Photo / Supplied

The punch knocked him out cold, causing his head to hit the pavement and the promising water polo player died in hospital two days later.

Renata has been in custody since January 3, 2016, after being arrested for the attack on Miller.

Since being in jail, Renata has been involved in a number of altercations with prison guards across Queensland.

Renata pleaded guilty to the charge earlier this week in Maryborough Magistrates Court and was sentenced to an extra three months in jail on top of his seven year sentence.

In an attempt to stop one-punch attacks like Miller's, Queensland introduced stricter laws that requires those found guilty to serve 80 per cent of their sentence.

Including time served, Renata is facing an extra one month in prison before being eligible for parole.

Renata has since been moved to Brisbane Correctional Centre where he is expected to serve out the rest of his sentence.

According to Fairfax, Renata was previously charged with assaulting three prison guards at Woodford Correctional Centre in April last year.

All three officers from the north Brisbane prison were taken to hospital, one with a broken arm, and discharged later that day.

A source told the publication Renata and another inmate were allegedly protesting overcrowding in the prison and started a "brawl".

The assault charges were eventually dropped and were replaced with two counts of assault or obstruct corrective service officer.

Renata pleaded guilty and was convicted but did not have any extra time added on to his sentence.

While Renata was the one who delivered the fatal blow to Mr Miller, it was his Kiwi accomplice Daniel Maxwell that hit the Brisbane teenager first.

Maxwell, now back in New Zealand, had tried to start three other fights while walking through the Valley before he and Renata came upon Cole and his friend Nicholas Pace.

Maxwell had said, "Do you want to see something funny?" before approaching the pair and punching Cole in the chest.

Including time served, Maxwell walked free from court in February after being given an 18-month suspended sentence.

When Miller's dad Steve saw Maxwell walk free from court, he put in a call to the Australia's Home Affairs Minister Peter Dutton's office.

The minister has taken a hard line tactic against foreigners committing crimes in Australia, deporting thousands of people for criminal offences.

Calling in to Ray Hadley's show on 2GB in February, Miller had a tearful message for the minister.

"I'd just like to thank Peter, last year an accomplice to my son's death who was killed in a coward's punch was sentenced to over 12-months jail … and there was a bit of a mix up at the courthouse and he was let to walk free."

"On that day at about 2pm, I was advised by a journalist that he'd walked free. I got on to Peter Dutton's office in Canberra, he was unavailable at the time, he was in Parliament, and he rang me back at 4.30pm," Miller said.

"He got on to the Queensland Police and Border Force immediately and that illegal immigrant was taken back into custody by 6.30pm that night and held for deportation to New Zealand.

"I'd like to thank Peter Dutton for that, he didn't know me from a bar of soap," Miller added.