CCTV footage shows Anneli Alderton travelling in the train between Harwich and Colchester, England. (Reuters)

London, Dec. 16 (Reuters): British police released surveillance television footage of one of five murdered prostitutes today as they stepped up their hunt for a possible serial killer.

The image of Anneli Alderton, 24, who was three months pregnant when she was murdered, shows her travelling on a train between the towns of Harwich and Colchester in eastern England on December 3, a week before her body was found.

All five prostitutes were naked when their bodies were discovered and police said the images were important for forensic evidence purposes, as well as trying to determine Alderton’s movements in the final hours before her death.

“I would ask people to look carefully at the images,” chief superintendent Stewart Gull said today. “If anyone saw Anneli after the evening of Sunday December 3, we want to hear from them.” Alderton was pictured wearing a black jacket with a fur-lined hood, a grey top and blue jeans.

The case has echoes of those involving the 19th century prostitute killer Jack the Ripper, who was never found, and Peter Sutcliffe, the Yorkshire Ripper, who killed 13 women, mainly prostitutes, in northern England between 1975 and 1980. The murderer has been dubbed the Suffolk Strangler, although the precise way all the women died is yet to be established.

Prostitutes in the region are being offered financial help to stay off the streets but some have ignored police warnings and carried on working, many to feed drug habits, despite the discovery of the five bodies in less than two weeks.

Prostitution in Britain is legal but there are laws that make providing sex for money difficult. For example, a woman can sell sex in an apartment, but advertising sexual services, streetwalking, brothels and kerb crawling are all illegal. About 350 officers are working on the inquiry and staff from more than 30 forces — including Northern Ireland — are trying to find the killer.