A taxi driver who killed a young office worker was "besotted" with a sex worker he is accused of murdering years earlier, a court has heard.
Christopher Halliwell, 52, is alleged to have strangled Becky Godden, 20, and buried her in a remote field in Eastleach, Gloucestershire, in 2003.
He is currently serving a life sentence with a minimum term of 25 years after admitting stabbing and strangling Sian O'Callaghan, 22, in 2011.
Bristol Crown Court has been told that Halliwell initially confessed to strangling Miss Godden and led police to the "exact spot" where her remains were.
Halliwell, formerly of Ashbury Avenue, Swindon, Wiltshire, has since pleaded not guilty to murder and is representing himself at his trial.
A former Swindon prostitute, referred to in court as Miss X, told the jury of six men and six women that Halliwell was a "regular" customer of Miss Godden.
Miss X said she knew Halliwell as "Chris" and would often see his car parked near Swindon's red light district, where she and Miss Godden worked.
"I would say 'Does he take you to score?' and she would say no, he was just one of her regulars," she told the jury.
"She did not go into much detail in the conversation on that occasion; we had another one and she was just like sometimes he does her head in.
"I'm not 100% sure but he was always parked there. That might have put the person off who's parking up to a girl.
"Nothing that rang alarm bells to me. He was always wanted her to go with him and stuff. He was just a bit besotted.
"To be honest, I think Becky used to use him for a lift to score and stuff but I think he might have seen a bit more than that and I think it might have done her head in.
"At first he would give her money to stop her from working."
Miss X claimed that Halliwell had been her customer on two occasions.
"I would obviously recognise him because I've been up close and personal with him," she said.
On the first occasion, they went to an industrial estate in Swindon, and on another they went to his flat, it was alleged.
During the second liaison, Halliwell showed Miss X images of "Thai brides" on his desktop computer, she told the jury.
Later, Miss Godden and Miss X took a lift in Halliwell's taxi to buy drugs, the court heard.
"He said 'Don't mention to Becks that I have seen you'," Miss X said.
She claimed that during a conversation with Halliwell, the taxi driver told her he could not always afford to give Miss Godden money.
During cross-examination, Halliwell insisted he had never spoken to Miss X before.
"I don't have to tell you how serious this matter is," he told her from the dock.
"Please take a good, hard look at me and confirm the person you are thinking of is me."
Miss X stared at Halliwell and replied: "It definitely is you."
Halliwell later told the court: "I've never seen that woman before ... it is a fairytale."
Miss X said: "I don't understand how he can sit there and say he doesn't know me. I'm a hundred, million percent sure."