Terrence Brown, 35, was convicted of the murder of Tina Doyle, 38, who was strangled and stabbed at the flat they shared in Weymouth, Dorset.
Ms Doyle died on 26 February last year. After returning their verdict, the jury heard that on 26 February 1989, Brown had strangled his then partner, Mary Button.
Nigel Pascoe QC, for the prosecution, said that on 9 November that year Brown was convicted of murder and sentenced to life imprisonment. The conviction was quashed in 1992. A verdict of manslaughter was substituted and he received an eight-year jail sentence. He had been in custody since his arrest and was released in July 1993.
Mr Pascoe said the conviction was quashed because during the trial it became clear there was a distant relationship between a juror and a police officer which should have been investigated at the time.
The verdict that Brown was guilty of Tina Doyle's murder was greeted with a shout of "yes!" from his first victim's relatives in the public gallery at Winchester Crown Court. Her sister, Janice Olwyn, mouthed "Thank you" at the jury. The killing left her sister's daughter Stacey, now 13 years-old, motherless.
"All we can get out of this now is justice at last and it's terrible for the other family," she said. "I want him away for ever and that's all Stacey wants."
Another of Mary Button's sisters had tried to warn Tina Doyle to stay away from Brown, who began living with the Port Talbot divorcee when she moved to Weymouth, but she disregarded the warnings. Ms Doyle's own sister, Patricia Snook, who knew Brown from Port Talbot, had also warned her to stay away from him.Reuse content