An intensive search and surveillance operation has been mounted on as few as five key suspects in the hunt for the Ipswich serial killer.

Detectives are increasingly confident that they are closing in on the murderer, who has dumped the naked bodies of five women around the edge of the Suffolk town.

One man in particular has come to the fore. A senior police source described him to The Times as “very interesting."

Despite the progress, the investigation is likely to be a lengthy and painstaking one as police amass sufficient evidence — especially from closed circuit television footage — to make an arrest. The movements of some of the prime suspects are being monitored closely but the exact whereabouts of others is not known.

Operation Sumac, the codename for the inquiry into the murders of Anneli Alderton, 24, Gemma Adams, 25, Paula Clennell, 24, Tania Nicol, 19, and Annette Nicholls, 29, is moving fast and the list of suspects is being constantly whittled down as information is analysed.

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They include known sex offenders from Suffolk and other areas, men who travel to Ipswich to pick up prostitutes and people associated with the drugs trade.

Police family liaison officers have told the family of Alderton, 24, whose body was discovered near the village of Nacton last Sunday, that she was in the early stages of pregnancy.

The parents of Nicol made a public appeal yesterday for information that would help to trace their daughter’s killer. Jim Duell, her father, appeared alongside Kerry Nicol, the dead girl’s mother, and described Nicol as “a caring, loving, sensitive girl” who was taken away by drugs “into her own secret world."

Duell said: “If anyone has any information, however small, please tell us.”

Police patrols, including vehicles with numberplate recognition technology, have been looking for cars and vans associated with the men on the suspect list. Recovery of the vehicle used in the murders is crucial to the inquiry because it may be not only the killer’s means of transport but the place where he murdered his victims.

The source said: “The focus of the inquiry has narrowed significantly. We are looking at a small number of individuals and are at a key stage of the investigation. There are a number of cars and other vehicles associated with these individuals and we are on the lookout for all of them.”

Police believe it is “very significant” that none of the bodies of the murdered women shows signs of injuries associated with a fight or a struggle and that none was sexually assaulted before being killed.

Their remains were found naked but in the cases of Nicol, Adams and Nicholls the killer left their bracelets, necklaces and rings on the bodies.

A post-mortem on Nicholls, the last of the victims to be identified formally, did not return a conclusive cause of death. However, detectives are proceeding on the assumption that all the women were strangled or suffocated.

There were fears that the killer might have struck again when another prostitute was reported missing last night. Police were alerted when the woman failed to check in with her probation officer. She was later found safe.

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