Prison advocates are appalled no one will be prosecuted over the death of Jai Davis.
Jai Davis, 30, died while on remand at the Otago Correctional Facility in February 2011 of a suspected drug overdose as he tried to smuggle drugs inside his body.
Police said on Tuesday they would not lay charges against prison officers or nurses over his death because there was not enough evidence and the breaches of his care were systemic.
The decision was made after Crown Law reviewed the case following damning evidence made public at an inquest last December.
The inquest heard there were many warning signs that Davis was sick in the days before he died but no guard or nurse sent him to hospital.
The Howard League for Penal Reform was among those pushing for prosecutions against those involved.
Spokesperson Madeleine Rose said the lack of action against anyone involved sent a terrible message.
"The concern is that it will lead Corrections officers and Corrections nurses to just believe they can do whatever they want."
Wellington human rights barrister Michael Bott said he was disappointed rather than surprised by the decision.
Corrections said 57 prisoners since 2004 have died of unnatural causes in custody but Mr Bott believed the number was closer to 90.
"So far no one's been prosecuted, no one's been held to account, and we get more of the same today. It's extremely sad that an inmate has died and his death almost went without demur until somebody made a complaint and kicked up a stink."
Nothing would change until individuals were held to account, which was still possible through a private prosecution or a civil claim, Mr Bott said.
Davis's mother, Victoria Davis, said yesterday she was looking into both of those options.
But the Corrections Association which represents prison officers said the police decision is fair.
Its industrial officer Beven Hanlon said staff were in a difficult situation.
"Corrections could have taken the step of getting the prisoner physically examined by a doctor. That's not putting him on a CT scan and scanning him - that's us holding him down while a doctor internally examines him. That's not a nice process. Now, if we'd done that to that prisoner and he didn't have something, there'd probably be a different conversation happening right now."
Mr Hanlon said Jai Davis created the circumstances of his own death.
"What we've got to remember here is that we've got a prisoner who we suspected had some drugs concealed internally. He was asked on several occasions whether he did, he claimed he didn't."
He said the suspected overdose was not the fault of the staff. "Let's be clear here - the prisoner did it to himself."
But Madeleine Rose said Mr Hanlon's claim didn't wash.
"Say you're dealing with a child and they say, no, I didn't take any poison, and you see them turning purple and you just leave them because they said they didn't, it just doesn't add up. There were very clear signs that he was really ill."
The coroner said yesterday his findings into Jai Davis's death were still a long way from completion but he expected to give adverse comment about a wide range of parties.