A sex attacker was jailed indefinitely yesterday after he was caught using DNA from a pair of sunglasses grabbed by his victim.
Jailing Duncan Turner at Birmingham Crown Court, Judge Richard Griffith-Jones said he represented a "significant risk" to women of serious harm.
The court was told Turner, who had previous convictions for sexual offences, left his sunglasses behind when he fled the scene and they were subjected to a special technique used in examining small amounts of DNA.
His DNA was recovered and police made a match on the national DNA data base.
Turner (44), of Station Road, Erdington, who pleaded guilty to a charge of sexual assault, was also ordered to register as a sex offender for life.
The judge said: "What you did in this particular case was appalling.
"It must be every woman's nightmare to be alone in a city, walking through a subway, and to be attacked by a stranger in the way you did. I have no doubt she thought something even more terrible was going to happen."
He said the victim was badly affected and continued: "It went on for some appreciable period of time. Your actions were forceful, frightening and persistent."
The judge also praised the woman for her courage and her initiative in spotting the sunglasses and the police saying: "This seems to have come to light because of very good police work and the use of modern techniques which must provide reassurance for the public."
Sally Hancox, prosecuting, said Turner was a married man with two young children who was self employed and travelled the country regularly in his work as a shop fitter.
She said his 21-year-old victim had gone to Birmingham city centre on August 28 last year, a bank holiday Sunday, to meet a friend and was walking towards the jewellery quarter at about 11.15am.
Miss Hancox said she decided to take a subway under Great Charles Street when she became aware of a man coming up behind her.
She said Turner put his arm around her face covering her mouth completely and put his other arm around her waist before forcing her to the ground.
Turner then told the woman, who was slightly built, not to struggle or scream or he would hurt her before sexually assaulting her.
Miss Hancox said during the attack Turner became increasingly frustrated and angry and the victim feared she would be raped.
She said the woman never saw the face of Turner who eventually ran away when someone else came down the subway.
She said police were able to prove using CCTV that Turner had driven into the city before the attack and they also recovered a receipt from his home for a pair of sunglasses bought as a replacement.
Miss Hancox said in November 1988 Turner had been jailed for three years for two charges of indecent assault one of them involving an attack on a 15-year-old girl at a city railway station while he had also been convicted of indecent exposure.
Sham Uddin, defending, said Turner had only intended to expose himself to his victim but became frustrated when she did not see him.