DETECTIVES are hoping that BBC's Crimewatch will help them nail the killer of teenager Jenny Nicholl.

And it is understood that the 19-year-old's mother, Ann Nicholl, will appear on the programme in the hope that someone, somewhere, will be able to solve the mystery of her daughter's disappearance.

It was also revealed last night that a substantial reward has now been put up to try to help solve the riddle which has baffled police for almost six months.

Several of Jenny's treasured possessions are still missing, including an aluminium box she kept her jewellery in and her silver CD/radio/cassette player.

Copies of the items will be shown by the presenters on Tuesday night, in the hope that someone will provide the vital clues to Jenny's whereabouts.

Officers from the Richmond investigation squad will be in the studio to take the calls.

Jenny's story is one the most mysterious cases police in the North have ever investigated and her disappearance has left them baffled.

She was last seen at the family home in Richmond, North Yorkshire, on June 30.

Detective Inspector Pete Martin will appeal on the show for information about the Co-op shop girl's movements between June 30 and July 4, the day she was reported missing.

He said: "As well as ongoing physical searches of rural areas around Richmond, we are concentrating hard on building up a picture of that crucial period - where she went, what she was doing and especially who she was with.

"I believe that someone out there knows where Jenny is and what has happened to her. We have always asked them to call us, or Crimestoppers on (0800) 555111 if they want to remain anonymous, but now there is the extra incentive of a large reward."

The programme will feature security camera footage of Jenny withdrawing cash from a Richmond bank shortly before she disappeared.

Det Insp Martin said: "We need to find Jenny's Nokia 5210 phone, from which spurious texts were sent in July.

"We also want to find the aluminium box Jenny kept in her bedroom to store jewellery and special possessions. We need to find her rucksack, which is grey with black straps, and we need to find her silver CD/radio/cassette player. We are not sure of the make, but it was an inexpensive model.

"This opportunity to appeal nationally for information is important to us. Our hope is that it will bring us the call we need to end months of stress, anxiety and pain."

The reward has been put up by Crimestoppers. It will be given for information leading to the conviction of any person or persons linked to the case.

Police are not revealing the amount of the reward, only that it is large.

The show will be broadcast on BBC1 at 9pm on Tuesday.

Officers will also staff a phone line in Richmond, which can be contacted on (01609) 768111.