Antoni Imiela had been jailed in 1988 for robbery offences

Even though his previous offences involved violent robbery, experts said the way he committed the sex attacks showed he was used to breaking the law.

His brazen attitude in raping a woman in a park only yards from a main road indicated to police that they would already have a record of the offender.

And detectives were also intrigued by the rapist's unusual habit of chatting to his victim and then stealing something from her.

Police turned to criminal behaviour expert Adam Gregory to construct a profile of the serial rapist responsible for nine attacks across the South East.

Mr Gregory works at the National Crime and Operation Faculty in Surrey, which was set up by the Home Office to log crimes and identify patterns of offending.

He said: "We looked at what he said, what he tried to get victims to say, how he established control and the way he left the scene.

'Rarely seen'

"The combination of Imiela's behaviours in most offences was rare.

"He was carrying out behaviours that were rarely seen in isolation, let alone combined.

"It provided almost a fingerprint identity of the offender."

The risk taking and the confidence were also indicative of a career criminal Adam Gregory, police adviser

Mr Gregory said: "The way he was establishing and maintaining control and the threats he was making were highly indicative of previous criminality.

"The risk taking and the confidence were also indicative of a career criminal.

"We were fairly confident this man would have had a history of criminality and inter-personal violence."

Imiela, 49, from Appledore, Kent, served nine years of a 14-year jail sentence after admitting a string of armed robberies or attempted robberies Durham, Yorkshire, Tyneside and London in 1988.

His crime spree started when he was 33 with the robbery of �10,000 from a post office in February 1987, during which he brandished a sawn-off shotgun and threatened to "blow the heads off" staff inside.

Police believe he then fled to Europe but returned in the autumn to carry out further offences.

A shot was fired into the ceiling in his attack on a sub post office that October.

And in November, he committed six robberies or attempted robberies, police said.

We had a very callous sexual predator - forensics was always going to be our big hope Asst Ch Con David Kelly

At the time, he was described by officers as "mysterious, deep and dangerous" and a person with separated Polish and German parents and an unsettled past, after spending most of his childhood in camps for displaced people in Europe.

For the forensic teams, the pivotal moment was when fibres found on a victim's clothing matched fibres belonging to the rapist.

The officer in overall command of the linked police investigation and former assistant chief constable of Kent Police, David Kelly, said: "We had a very callous sexual predator - forensics was always going to be our big hope.

"He (Imiela) did have some awareness of forensic investigation and he tried to hide his steps, but he made mistakes.

"If only he was on the DNA database, we could have arrested him immediately, but he wasn't.

"We would all welcome an expansion of the database - for not just current offences but also to go back in time."