Kate Bushell (pictured) was 14 when her throat was slashed near Exeter, Devon

Detectives who investigated the brutal murder of a schoolgirl 20 years ago have come out of retirement to follow a major new forensic lead.

Kate Bushell was 14 when her throat was slashed as she walked her neighbour's dog along a quiet country lane 300 yards from her home.

The killing, which took place on a Saturday afternoon in November 1997, shocked the nation due to its severity and apparent randomness.

No one was ever caught, despite a manhunt and a £1million investigation.

The hunt for Kate's killer is now the biggest ever murder probe by Devon and Cornwall Police.

Ahead of the 20th anniversary of Kate's murder, the force has reassembled original detectives who worked on the case in an effort to finally snare the killer.

The move is reminiscent of the TV drama New Tricks, in which retired officers tackle unsolved crimes.

Among those who worked on the original case are detectives Steve White and Paul Burgan, who is also a former head of Devon and Cornwall Police major crime unit.

As part of the new police appeal, Kate's eldest brother Tim has spoken for the first time about his family's ordeal.

Mr Bushell, who was 15 when his sister died, said: 'I have memories of the day, where I was and what happened throughout the day and being told I would never see my sister again.

It is very hard to relive those feelings because they were so difficult and completely changed my life and my family's life from that day.

'I think when you have got anniversaries coming up they are quite poignant and bring up memories you've had before.'

Detectives are sifting through new forensic evidence, which shows that Kate's body was covered in more than 100 fibres from bright orange clothing likely belonging to the murderer.

Tim Bushell (pictured), Kate's brother, has spoken out ahead of the 20th anniversary appeal to find the person who killed the 14-year-old as she walked a neighbour's dog near their home

Devon and Cornwall Police's superintendent Paul Burgan holding a kitchen knife which is believed to be similar to the weapon used to murder Kate Bushell

The fibres come from workwear such as boiler suits, aprons and gloves. Another fibre was found on a stile close to where Kate's body was discovered in Exwick, near Exeter.

Mr Burgan, senior investigating officer, said: 'These fibres are completely alien to Kate and her home. They were almost certainly deposited by the offender.'

He added that specialists are testing the fibres to try and extract the killer's DNA, and has called for witnesses who may have seen a man wearing such clothing at the time of the murder.

Police have also published a new picture of a 1.5in by 4in knife similar to the murder weapon which delivered the single, catastrophic wound to Kate's neck.

The teenager was last seen in a layby close to where she was killed, at 4.50pm on November 15, 1997.

Kate is pictured at home in Exeter before her brutal and shocking murder that still remains unsolved

Officers are also appealing for witnesses regarding several key people who have never been traced. One was a driver of a blue car parked in stables nearby who would have been in Kate's line of sight.

Detectives have also never established the identity of a man seen running manically through a field into a nearby housing estate at around the time of the murder.

Another potential clue is the location of Kate's body. The schoolgirl was found in a rural cut-through between the estate and a small village.

Detectives said it would be very unlikely for the killer to stumble on the lane because it is isolated and only known to locals.

Kate Bushell's father found her body in a field yards from their family home in Exeter (pictured)

The killer may not have been living in the nearby estate at the time but may have lived there, worked there, or known someone who did, police said.

Mr Bushell has appealed for anyone with information about his sister's murder to contact the police.

He said: 'Obviously a lot could have changed in the past 20 years – relationships they had and they felt they wanted to shelter or protect someone before, or they had a few doubts.

'Loyalties change and I would urge them to come forward and contact the police.'