The sister of a murdered airwoman has begged for help solving the crime 50 years after she was strangled with her underwear.

Speaking on the anniversary of the death of Rita Ellis, her sister Tina Streeter has reissued a plea for anyone with information to come forward to help catch her killer.

She was just 10 when Rita was murdered at the age of 19, on November 11 1967.

Her appeal comes as news DNA evidence has helped to eliminate just under 200 potential male suspects in the cold case.

Speaking yesterday Sussex nurse Mrs Streeter, 60, said: "It's been a long time coming but we want justice for Rita.

"Someone, somewhere must have some information."

Miss Ellis was sexually assaulted and strangled with her underwear at RAF Halton in Buckinghamshire.

Technological advances mean detectives have a full DNA profile of the murderer, but it has so far not matched anyone on the national database or any of the people swabbed.

Mrs Streeter added: "After Rita died I used to read the newspaper cuttings and it used to give me nightmares. I tried to understand it but I just kept thinking about whether she suffered - those things went through my head, even as a 10-year-old.

"Rita's murder has had a huge impact on me and my family.

My mother and Rita were incredibly close, they were like sisters. My mother was never the same after Rita died, my mother had a number of illnesses and, incidentally, she died on the same date (November 11) as Rita in 1994."

The nurse, who now works in Sussex, said: "Rita was wonderful. She was so kind, so caring, and so supportive, but she seemed to be frightened of certain situations and used to scare quite easily.

"She was painful shy, so going into the RAF was great for Rita because it broadened her horizons and gave her the confidence which she didn't have.

"I urge them to please come forward to the police and give us closure and allow Rita to be at peace."

She was supposed to babysit for a wing commander and his wife, but she was not at their agreed pick-up point.

Hundreds of people were on the base that night attending a disco and bingo.

Miss Ellis, who was stationed at the camp, was last seen alive at 8pm on the Saturday in her accommodation near Aylesbury.

Her body was found the next morning by a dog walker near a disused railway in the area.

Police believe the offender was a young man, possibly in his teens to mid-twenties, making him in his late fifties to eighties now.

Peter Beirne, head of the Thames Valley Police major crime review team, said officers suspected the culprit confided in someone and urged anyone with information to come forward.

A number of arrests were made at the time of the murder, but no-one has ever been charged.