Dissident republicans did not commit a criminal offence when they singled out doctors and nurses working at Maghaberry Prison, the PSNI Chief Constable has said.
Republican prisoners hit out at what they said was a "cosy relationship" between South Eastern Health and Social Care Trust staff and prison officers, warning health workers they "would do well to take note" of dissident gripes over their treatment in Roe House at the Co Antrim prison.
They also claimed they were getting "substandard" treatment over the time they have to wait for health appointments.
The prisoners' comments were described as "extremely sinister" and "disgusting".
The trust said it was "outrageous" for prisoners to target its staff, who they described as "ordinary, dedicated individuals".
Police had been urged to investigate the threats.
But it has emerged they are to take no action against those behind the remarks -- a stance strongly criticised as "not good enough" yesterday.
Chief Constable George Hamilton told members of the Policing Board: "PSNI has carefully considered the content of the document referred to in order to establish if any matters of a criminal nature exist.
"It is our opinion that there is nothing within the words articulated to indicate any criminal conduct.
"Nonetheless, PSNI would stress that in the event anyone is of the opinion that their personal security is, or may have been compromised, then we do ask that they bring all available information to our attention at the earliest opportunity. We will continue to monitor the situation in the coming weeks.
"Beyond that, and as is the norm, we cannot comment on the personal security of any individual."
Policing Board member and DUP MLA Jonathan Craig said he was angered by the decision.
"Here we have a very clear case of those within the health service having implied threats against them because they carried out their job," he said.
"It's not good enough for us as a society to say that's okay. The Chief Constable's response to this, while it angers me, doesn't surprise me."
Mr Craig there was a "lack of knowledge" of cyber crime within the PSNI and police forces across the UK.
"What this highlights is the question over how these cleverly-worded threats are interpreted by the PSNI," he said.
"I've pointed this out to them on numerous occasions. When written content appears on some of these websites those responsible are immediately open to several forms of legislation which opens them to possible court action. When something is published on a website it seems to have a much, much higher evidential threshold."
Carried on Republican Network for Unity's website - a group closely aligned with Oglaigh na hEireann - 'Republican Political Prisoners', said: "In the coming weeks the spotlight will be shone on all aspects of health care relating to prisoners. Those with responsibility for health care, staff and the treatment of prisoners would do well to take note." Health care inside the prison is provided by the South Eastern Health and Social Care Trust.
Last month the Belfast Telegraph revealed the threat to medical staff working at Maghaberry Prison. There are currently around 50 dissident prisoners inside Maghaberry.
The trust responsible for health provision in Northern Ireland's prisons said its staff were "upset and distressed" by intimidating remarks made by a republican prisoners' group. A health trust spokeswoman said staff "are ordinary, dedicated individuals working in caring professions, for the good of their patients". Earlier this year, letter bombs were sent to named members of prison staff at the jail.