Killer needs to increase the risk to maintain the thrill

The serial killer may be deliberately "taunting" police, a forensic psychologist has said. Dr Keith Aschroft, who was trained by FBI profilers, said the sudden infamy of the killer may feed his ego and compel him to kill again.

"He probably has some massive grudge against a police force, probably even Suffolk," Dr Ashcroft, who runs a private practice in Manchester, said. "He wants to make the police look inadequate because they are arriving after the bodies are being discovered. I really think that the media coverage is feeding this guy's ego and he is more likely than not to see the news and kill another person."

He said the way in which the bodies had been dumped in Suffolk suggested the killer had good local knowledge and was well aware of forensic science. "The fact that clothes have been removed, and bodies left in the water, shows some attempt to minimise DNA evidence," he said.

Dr Ashcroft said the case bore some resemblance to the 48 murders committed in Seattle by Gary Ridgway in the 1980s. Ridgway had been "obsessed" with prostitutes: "It was like he was getting his own back on the women in his life by murdering prostitutes, vulnerable women he could have power over," he said.

Dr Ian Stephen, a consultant forensic psychologist who helped police on previous cases, agreed that the fact the women were from the same area suggested that he might have a distorted image of women from Ipswich. "He maybe had a mother who has let him down, or a mother who has abandoned him," he said.

Britain's worst serial killers

Harold Shipman

Britain's most prolific killer took between 215 and 260 lives in the 1970s and 1980s, mainly elderly women in Manchester, where he was a GP. He was caught after forging a will, and convicted of 15 murders. The judge recommended he never be released. In 2004, Shipman, 57, hanged himself in his cell.

Fred and Rosemary West

Over 20 years, Fred and Rosemary West abducted, tortured, raped and murdered up to 30 women, picking them up from bus stops near Gloucester, and burying many in their home at 25 Cromwell Road. Fred West committed suicide before trial and Rose West was convicted of 10 murders in 1995. She is serving life.

Ian Brady and Myra Hindley

The Moors murderers, Myra Hindley and her lover Ian Brady, abused and killed five children and buried them on moors near Manchester. In 1966, they were jailed for life. Hindley died in 2002.

Peter Sutcliffe

For nine years, Sutcliffe spread terror in red-light districts across Yorkshire, using a hammer to kill mainly prostitutes. In 1994, he confessed to 13 murders and is serving life.

Dennis Nilsen

Over five years, Nilsen killed and dismembered 15 men lured from bars to his flat in London. In 1983, he was jailed for life for six murders.

Colin Ireland

In 1993, Colin Ireland, a former soldier, tortured and killed gay men he met in bars in Essex and London. He was convicted of five murders and is serving life.

Geneviève Roberts and Ian Herbert