The woman was found on Wednesday, at Coleby, five miles south of Lincoln. She had probably been beaten, and the killer had wrapped her in a blue, grey and pink checked duvet, then dumped her in a 5ft-deep dry dyke.
She was in her early twenties, and the best clue forensic scientists could give detectives was that she recently had dental treatment. She had been dead several days.
Four days earlier, Sharon Harper's body was found in Grantham, 25 miles south of Coleby. She was 21 and a barmaid at the Market Cross pub in town. She left work in the early hours of Saturday morning, and was strangled half a mile from home and just over a mile from work. Her body was dumped in an ornamental shrubbery in a car park.
'We can't link the two killings until we know who was the woman found in Coleby,' a Lincolnshire detective said. 'By the same token, we can't ignore the sequence of killings elsewhere.'
They began in December, when Samo Paull, 20, was found nearly naked in a ditch five miles north of Rugby, Warwickshire.
In March, the naked body of Tracey Turner, 30, was found at Bitteswell, south of Leicester.
Emma Merry, 18, was killed in May. She was strangled and stripped, then dumped on an industrial estate in Burslem, Staffordshire.
In May, Dawn Shields, 19, was strangled. Her naked body was found on Mam Tor in the Peak District. She, like the previous three victims, was a prostitute.
All were found a few miles from where they worked. Ms Paull solicited in Balsall Heath, Birmingham, Ms Merry in Burslem, and Ms Shields in Broomhall, Sheffield. Ms Turner sold sex at motorway service stations.
Lincolnshire police said Sharon Harper had no convictions for prostitution. She had a steady partner, and a regular job at the pub. A post- mortem examination revealed she had sexual intercourse shortly before her death.
The Lincolnshire investigations are to pool information with colleagues in Leicestershire, South Yorkshire, Staffordshire and the West Midlands.
The woman found in Coleby wore two silver rings on the middle finger of her left hand, one a band, the other a heavy, latticed design.
She was white, had a pale complexion, was 5ft 8in and of slim-to-medium build. She wore her very thick dark brown hair shoulder length. Both ears were pierced, but she was not wearing ear-rings.
Information about the Coleby victim may be given to Lincoln police on 0522 529911. Information about Sharon Harper may be given to Grantham police on 0476 62501.