Yorkshire Ripper Peter Sutcliffe admitted carrying out two undisclosed attacks on women during the late 1970s, it has been revealed.
Sutcliffe claimed at his trial that "voices" told him to kill
The mass murderer admitted his involvement to detectives who spoke to him after his trial in 1981.
Prosecuting officials decided it was "not in the public interest" to pursue the attacks through the courts.
A West Yorkshire Police spokeswoman said the female victims wanted to remain anonymous.
A West Yorkshire Police spokeswoman said on Thursday: "Following conviction, Sutcliffe was interviewed about two other assaults.
"Information about these matters was considered by the force prosecuting solicitor, but it was not considered in the public interest to prosecute.
"The two victims asked for no publicity about the matters, therefore we are not in a position to reveal further detail about them."
The spokeswoman added that there was currently no evidence linking him to any other offences.
Sutcliffe, 58, is serving life for the murders of 13 women in West Yorkshire between 1975 and 1981.
Seven others were left for dead in a spree which terrorised the north of England.
Last month he was allowed out of Broadmoor top-security hospital to visit Arnside in Cumbria where his late father's ashes were scattered.