The middle-aged man from north Dublin, who was questioned about the double rape of two prostitutes in a Ballymun hotel, recently walked free from court.
He had been facing charges of harassment in relation to two female sex workers who accused him of raping them in a hotel last summer.
Ten days before he allegedly raped the foreign sex workers, the man was stopped while he was driving in van, which contained duct tape and cable ties.
He had previously been stopped carrying a knife and knuckle-duster.
A senior source said: "This individual is capable of murder and there are fears that this is exactly what he will do. This individual is the number one danger against women -- particularly prostitutes -- in this country.
"He is a suspect in over a dozen rapes and he is extremely violent but also very cunning.
"There are major concerns at the moment about the safety of alleged injured parties -- this individual is so twisted that he could go looking for revenge because they talked to gardai."
The suspect was released from prison -- where he had spent the past two months -- after a judge struck out charges at a district court hearing this week.
The man, who lives on the north side of Dublin, is facing separate charges in relation to a campaign of terror against gardai in a rural location.
Gardai have not yet been able to build enough evidence against the suspect in relation to the alleged double rape in August.
The women -- who were picked up by the man in a van in Dublin city centre on August 10 -- were brought to a hotel in Ballymun.
While there, they alleged that they were given a substance and then savagely sexually assaulted.
The women went to Ballymun Garda Station the following morning, where they made a formal complaint.
They were then taken to hospital and investigators are still awaiting the results of forensic and other tests that were carried out on the women.
Some time later, the suspect voluntarily attended the station, where he was interviewed by gardai. He was not arrested.
The man stated that he had sexual intercourse with both women, but denied that he had raped them.
Specialist detectives from the garda domestic violence and sexual assault investigation unit have been probing links between the alleged Ballymun rapes and other attacks on prostitutes in Dublin city centre.
Sources say that "certain links" have been made in up to a dozen cases.