A scientific breakthrough which could solve one of Britain's most baffling murders may be just months away, investigators said last night.

On the eve of the 13th anniversary of the killing of housewife Ann Heron, whose body was found at her home on the outskirts of Darlington, the new detective leading the case vowed that justice would be done.

The 44-year-old was discovered by her husband, Peter, lying in a pool of blood at Aeolian House, near Middleton St George, on August 3, 1990. Her throat had been slashed.

Despite 4,000 witness statements being taken and 1,500 exhibits collected from the scene, her killer has never been caught.

However, Detective Superintendent Dave Jones said tiny samples which could point to the culprit were being held by forensics specialists - and that the technology to carry out delicate examinations on them was not far away.

Promises of a breakthrough have proved unfounded in recent years, but the murder team is now said to have a "genuine hope" of ending the long-running inquiry.

"The encouraging thing from our point of view is that we see, almost weekly, cases that have been unsolved for 20-odd years throwing up new evidence and people being arrested and convicted," said Det Supt Jones.

He said scientists had indicated that staggering advances in DNA profiling could soon provide a significant lead.

"I believe one day the staff at the laboratories, using techniques at the very forefront of technology, will ultimately provide information that will point to the killer," he said.

Detectives are still trying to trace a sun-tanned man, aged 35 to 40, who drove a blue car at speed down the driveway of Aeolian House at 5pm on the day of the killing.

A man spotted jogging along the A67, which runs past the entrance to the driveway, has also not been traced.