Newshub can reveal one of Rimutaka Prison's highest-ranking custodial officers has been suspended for "alleged serious misconduct".
The staff member is one of four employees that have been stood down, amid an inquiry into corruption at the jail.
Official information shows there have also been several resignations at the prison since detectives began working on the case.
It's our most populous prison and is the focus of a major police investigation.
Under suspicion is one of the principal Corrections officers, or 'PCOs' at the jail - who's been removed from duties.
"So they're the highest-ranking frontline custodial officer we have. After that you rise into the ranks of management," says Corrections Association vice-president Paul Dennehy.
"It's unusual for a PCO to be involved in an employment investigation and suspended."
Newshub understands the police investigation relates to smuggling contraband including cellphones and drugs into the prison, money laundering and altering official documents.
The police investigation began in July. In the 10 weeks to September 11, official information obtained by Newshub shows a PCO was suspended for "alleged serious misconduct".
A Corrections officer was also suspended over the same allegation. And four other staff, including a Corrections officer, admin support officer, a psychologist and programme facilitator have resigned.
It's not known if the resignations relate in any way to the current police inquiry.
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Dennehy says most Corrections staff are professional and hard-working.
"As with any organisation or any part of society, there are those small few who are corrupt, not abiding by the laws, letting everyone else down and they tarnish everyone," he says.
Newshub's Official Information Act request only captured up to September 11.
However, Corrections says that since then two more staff at Rimutaka have been suspended.
It's not known what roles they played. All four employees who have been suspended remain on full pay.