Teenage killer Kieran Loveridge has been moved to the state's highest security prison after having an "improper relationship" with a female guard, just a week after he allegedly stomped on the head of another prisoner.
Loveridge is serving a minimum of 10 years for the manslaughter of Thomas Kelly, who was punched once on the back of the head on his first night out in Kings Cross in 2012.
Loveridge was also convicted of a string of random assaults on the same night.
2GB broadcaster Ray Hadley revealed on radio last week that Loveridge, now 21, was being investigated by police for allegedly stomping on the head of an inmate in a Kempsey jail on March 10.
Loveridge and another inmate, aged 22, allegedly assaulted the 31-year-old man in a cell. He had to be treated for facial injuries in Kempsey Hospital.
The two inmates were segregated, moved to other jails and given higher security classifications, a Corrective Services NSW spokesman said.
On Thursday, Hadley revealed Loveridge had been moved to Goulburn Supermax and prison officials were also investigating an affair he was having with a female guard at the Mid North Coast Correctional Centre.
"A female correctional officer has been suspended from duty at Mid North Coast Correctional Centre after it was learnt she had allegedly commenced an improper relationship with an inmate," the Corrective Services NSW spokesman said.
"CSNSW is investigating the alleged relationship."
Hadley said other prison guards raised the alarm after they noticed odd behaviour between the pair.
Loveridge was initially sentenced to five years and two months for manslaughter but it was raised to a minimum of 10 years after the Director of Public Prosecutions appealed against the "manifestly inadequate" sentence.
Mr Kelly's death caused public outrage and partly led to the introduction of mandatory sentences for drunken violence and a state-wide liquor crackdown.
Loveridge could remain in jail until 2026.