Death threats have been made against the Australian radio hosts involved in the royal prank call case, police said on Friday, with station management reportedly moving some employees to safe houses.
The revelations came as a London investigation showed the nurse who fielded the hoax call, Jacintha Saldanha, 46, hanged herself.
The mother-of-two was found dead last Friday, three days after transferring the call to a colleague who divulged details about Prince William's pregnant wife Catherine who was recovering from severe morning sickness.
Saldanha was discovered in the nurses' quarters near the private King Edward VII's Hospital in central London where Kate was being treated. She also had wrist injuries and left three notes.
Australian police have launched an investigation into the death threats after a letter targeting presenter Michael Christian was seized, warning him there were "bullets out there with your name on it".
The letter was obtained by Sydney's Daily Telegraph, which said further threats were made involving a shotgun.
The Australian Broadcasting Corp said employees at 2Day FM's parent company Southern Cross Austereo have been receiving threats all week.
"Police are conducting an investigation into threats made against two Sydney radio presenters," a New South Wales police spokesman said.
"Detectives seized a letter which contained a number of threats. Detectives are conducting an investigation into the matter and are attempting to identify the source of the letter."
The Telegraph said about a dozen employees at the broadcaster have been moved to hotels for their safety and up to 10 executives have been assigned bodyguards.
Southern Cross Austereo would only say that "the safety of our employees is an absolute priority".
The broadcaster's spokeswoman said: "We have sensible measures in place, as we always do, to ensure our people are safe."
Christian and fellow host Mel Greig, who have been undergoing counseling, remain off air and have not been seen in public since making tearful apologies in a television interview on Monday.
The radio station has pledged at least A$500,000 ($523,600) to help the grieving family, although British lawmaker Keith Vaz, who has been acting as their spokesman, said the broadcaster had not done enough.