Police issued an alert after the latest grisly find near Ipswich, some 80 miles (130 kilometres) northeast of London, advising all prostitutes to stay off the streets for their own safety.
"Clearly this is a deeply disturbing development, particularly in light of the two murder investigations already underway," said Detective Chief Superintendent Stewart Gull, who is heading the inquiry.
"While we can't formally link the discovery with the two murders, the facts speak for themselves," he told reporters Monday.
Asked if a serial killer was at large, he replied: "Yes, it's possible."
The first two murdered women -- Gemma Adams, 25, and 19-year-old Tania Nicol -- went missing in the red light district of Ipswich, near the eastern coast of England, on November 15 and October 30 respectively.
Adams's body was found in a brook at nearby Hintlesham on December 2, while Nicol's was discovered on Friday at Copdock, in the same stretch of water about two miles (3 kilometres) away.
Detective Chief Inspector John Quinton said Sunday the two murders were "strikingly similar", and added police were working with experts to build up a profile of who might be behind the killings.
There were no obvious signs of violence to their bodies, but it appeared that the same person or group were involved in both deaths, he said.
Within hours, it was confirmed that the body of a third prostitute, also in her 20s, had been found in woodland near the village of Nacton outside Ipswich, fueling concern about a killer targetting sex workers.
Then on Monday, police announced that a fourth prostitute was reported missing.
She was identified as Paula Clennell, 24, who has not been seen since late Saturday.
Assistant Chief Constable Jacqui Cheer issued a stark warning to other prostitutes in the area.
"Please stay off the streets. If you are out alone at night, you are putting yourself in danger at this time," she said.
More generally, she said all women should be concerned, especially as the Christmas season is starting.
"We're coming up the party season .. There will be groups of young women, young people going out. What I would say to them is, you have really got to look after each other," she said
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