It was a sunny Sunday morning when serial sex attacker Duncan Turner pounced on his latest victim in a subway in Birmingham.
Turner bought a replacement pair of sunglasses on the same day
He assaulted the 22-year-old woman and threatened to rape her, only fleeing when he was disturbed.
But Turner, 44, left behind a pair of sunglasses which his victim picked up and handed to police.
It was a vital clue that eventually trapped Turner, who has a history of sex attacks dating back 18 years.
He pleaded guilty to sexual assault in February and was jailed indefinitely on Wednesday. He will not be considered for parole for two-and-a-half years.
"For the first couple of hours I was just hysterical," said his victim as she recalled the day of the attack.
1988 four indecent assaults
1991 indecent exposure
1996 indecent assault
"I was trying to come to terms with what had happened to me."
When the sunglasses were sent for forensic examination two DNA sources were blended together.
But experts used new techniques to separate the DNA which helped them identify Turner, whose details were on a national database.
Forensic scientist Kate Jones said: "I hope this shows we are constantly coming up with new techniques to look at DNA and utilising the DNA database in different ways.
"I hope it sends out a message [to sex offenders] that we are going to find them eventually."
Turner struck in this subway on a Sunday morning
The DNA on the sunglasses helped prosecutors build further evidence against Turner.
Automated number plate recognition tracked a car leaving Turner's home in Sutton Coldfield, travelling into the city and then leaving again after the offence.
Turner, who ran his own shopfitting business, was also found to have bought a replacement pair of sunglasses in Cirencester, Gloucestershire, later on the day of the offence.
Martin Lindop, the senior crown prosecutor in the case, said: "It is a case in which 20 years ago police would never have caught anybody.
"We rely on the scientists to tell us how unique DNA is.
"And that evidence left us being able to present an overwhelming case to the court."
There are large gaps in Turner's offending and criminal experts believe he could have struck at other times.
"He may well have gone on to commit further serious offences. Obviously he will no longer be able to do so," said Det Sgt Trevor Robinson, of West Midlands Police.
His latest victim said the case should give hope to other sex attack victims.
"The glasses helped me to live with the fact this guy is now going to prison and I know it is the right person.
"It shows to other people that go through similar things that there are ways of catching these people which isn't necessarily your word against their word."