Cold case detectives are re-investigating a 36-year-old unsolved murder using the latest scientific forensic DNA techniques.
Evidence from the crime scene including her clothing is being re-examined in Forensic Science Service laboratories.
Avon and Somerset Police's major crime review team are also making a new appeal for information.
Television presenter John Craven, who reported on the case for BBC Points West news at the time of the murder, has returned to the scene of the crime to investigate for the BBC programme Inside Out West.
Detective Chief Inspector Mike Carter told him: "Forensic advances have moved on so much that we are hoping to get a profile which we will then compare with those on the national database.
John Craven interviews Det Ch Insp Mike Carter about the murder in Bristol in 1974
"The person who murdered Glenis Carruthers may have thought he had got away with this after all these years but we are determined to try to track him down."
Dr Colin Dark, senior forensic scientist, said: "In 1985 when DNA was first introduced as a technique we had to deal with body fluid material but there have been significant advances in the sensitivity of the processes.
"Now we can get DNA profiles from stains that we can't even see and we can also look for contact-style DNA where someone has just touched an object."
Glenis Carruthers was training to be a PE teacher at a college in Bedford and was visiting Bristol for the weekend to attend a friend's 21st birthday party given by her family at their home in Clifton.
No-one saw her leave the house but it is believed she decided to walk to a telephone box near the downs more than half a mile away. Her body was found on a patch of grass alongside a lane in front of Bristol Zoo.
Glenis's older brother Gordon, who was 30 at the time of the murder and is now in his 60s, said her family and friends had suffered years of distress since the murder.
"My appeal would be to whoever knows about this or knows the person concerned who carried out this terrible act that they now do the right thing and come forward because although time has elapsed the memories have never faded.
"We want justice for Glenis and then we can let her memory rest in peace."
