Susan Nicholson was murdered by her partner in 2011
Peter and Elizabeth Skelton spent six years and £10,000 of their own money fighting for justice after their daughter’s murder.
Speaking to BBC Radio 5 live, Mr Skelton said "when you know somebody was murdered, you never give up on them."
Robert Trigg was sentenced to a minimum of 25 years in prison earlier this month for the murder of Susan and the manslaughter of Caroline Devlin, another of Trigg’s ex-partners.
Speaking after the trial, judge Mrs Justice Ingrid Simler said Mr and Mrs Skelton had "fought doggedly and continuously since their daughter's death for the police to re-investigate her death".