A murder case is never completely closed until an arrest is made. Tonight police reveal their current investigation into a crime which happened 20 years ago. Two girls, Barbara Mayo and Jackie Ansell-Lamb, were murdered near the M1 and M6 after hitch-hiking north. With viewers' help, officers believe they can now solve the case and close their files at last.

At 39 Derrick Johnson was a happy family man. He always phoned his son if he had to work late in Canning Town, east London. But on Tuesday 6 November there was no phone call. Derrick Johnson had been murdered. Police appeal for help on this and other serious crimes.

Detectives want to trace all taxi driver Steve Johnson 's passengers in Stoke-on-Trent on the evening of Friday 21 December. One of them decided to kill him. Perhaps you were shopping in Cheltenham on Wednesday 30 January? If so, you may have seen a gunman and his accomplice. And Maria Requina from Manchester was murdered only weeks after talking on TV about the dangers of street life.

Inventor John Green was murdered at his home in Poole. Dorest detectives need your help to find two men seen scuffling with him in the street. And who did he arrange to meet at a roadside cafe just days before his murder? If you can help, phone lines will be open on [number removed]from 9.00pm until midnight. If you witnessed an armed robbery would you be able to identify the robbers? At the start of Crime Prevention Week Crimewatch UK stages an armed robbery and tests three viewers on their observational powers. Could you do better?

Alan Leppard had spent Easter Monday happily at home with his girlfriend in the quiet village of Monkton, Kent. That night he was shot dead on his own doorstep. Could you have seen his killers in a large American car?

The Dorset force are still searching for Jo Ramsden , who has Down's Syndrome and disappeared from the centre of Bridport on 9 April. The Metropolitan police want to find the gunman who shot antiques dealer, Peter Rasini. Ring [number removed]if you can help.

Twenty-four hours after vanishing from her home in Leeds, teenager Julie Dart wrote a letter to say she had been kidnapped. Ten days later her body was found 90 miles away in Lincolnshire. But from clues left behind by her killer police have now compiled a psychological profile of the man they hope viewers will recognise. Businesswoman Penny Bell was murdered in broad daylight in the car park of a west London swimming pool. Did anyone see the smartly dressed man leaving her Jaguar car?

A policeman was fired at by a bank robber making his getaway in Suffolk. And in Essex, a supermarket manager and his family were held hostage.

At 12.20am on 29 June, Paul Griffiths found the battered body of his father. Seconds earlier Paul had seen a man heading towards Cricklewood Broadway: viewers may be able to identify him. Someone may know the whereabouts of Andrew Elphick, missing since August and feared dead. And long-distance lorry drivers may hold the key to the murder of 42-year-old Vera Anderson.

This year, on 1 October, Marion Rilka was brutally stabbed in the hallway of her home in Hove, East Sussex. Detectives have very little evidence and can find no motive for her murder, but a woman living nearby remembers a strange, menacing man she turned away from her door less than an hour before Marion was killed. Detective Chief Inspector Tim O'Connor from Sussex police, is in the studio with the latest news of the investigation.