“Two hypnosis experts have been mobilized to dig into more clues and help revive memories that may have been lost or altered over time,” the agency’s Superintendent General Ban Ki-soo explained.

Thursday’s update came a week after police identified a prime suspect -- a 56-year-old man surnamed Lee -- following a National Forensic Service test that confirmed his DNA matched that found at three of the rape-murders.

Lee is suspected of at least eight rape-murders that took place over the span of five years from 1986 to 1991.

Police said a team of profilers visited Lee, who is serving a life sentence for the 1994 rape and murder of his sister-in law, for the fifth time Wednesday.

While there was no admission of guilt from Lee, “profilers are working on establishing close rapport with the suspect, who is entitled to refuse police visits, as the cases’ statutes of limitations expired in April 2006,” said Ban, who is leading the probe.

Ban said Lee had come under suspicion while the case was still ongoing, and was questioned three times between 1987 and the early 1990s.

Lee was released, however, as two key pieces of evidence at the time -- the size of a footprint and blood type -- did not point to him.

“Footsteps imprinted in the crime scene were measured to be between 245 and 255 millimeters, and the blood group test on a sample collected from one of the victims’ clothing was interpreted as type B,” Ban said. “Both did not match Lee’s.” He added the blood type was later discovered to be an error.

Police are also looking into other unsolved crimes that took place in Hwaseong and the surrounding area from the year the first murder occurred, 1986, to 1994, the year Lee was caught for the rape and murder of his sister-in-law. Lee was sentenced to life in prison in 1995.

On Tuesday, police said Lee could be linked to seven rapes reported between February and July 1986, only a few months before the first victim of the serial killing was found the same year on Sept. 15.

Ban said police are approaching the three-decade-old case “from ground zero,” and re-examining “vast volume of records accumulated over the years.”

Meanwhile, Lee’s full identity was released for the first time by a local broadcaster Wednesday. Police said they would review the legal basis for posting Lee’s identity after his guilt is confirmed.

By Kim Arin (arin@heraldcorp.com)