Police have re-opened an investigation into the murder of a schoolgirl 50 years ago.
Elsie Frost, 14, was stabbed to death on a canal towpath in Wakefield in 1965.
Detectives have launched a public appeal and are seeking information about a "butcher or abattoir worker" who was seen cycling near where she was found dead.
Officers also want to identify someone "possibly a boyfriend" who may have been meeting Elsie in secret in the days before her death.
Detective Chief Inspector Elizabeth Belton said: "Elsie's death may be many decades ago, but the pain of her loss remains as fresh as ever for her brother Colin and sister Anne.
"Her brutal murder shattered their family and with such a significant anniversary near, I would ask anyone who may not have come forwards then, for whatever reason, to do so now and provide them with answers."
She added: "We now believe at least one person, who was never interviewed at the time, was seen near the location where Elsie was murdered on the canal towpath.
"He was described as white, 25 to 30 years old and riding a black bike with a basket on the front and wearing a white lab type coat possibly of the style then worn by someone who could have been a delivery boy, butcher or abattoir worker.
"Inquiries also suggest that when staying at a friend's a couple of weeks before the murder Elsie got dressed up and went out, possibly to meet someone.
"Elsie's murder may be nearly 50 years old but it is a crime people in Wakefield have never stopped talking about."
The re-investigation of the case was reportedly prompted by a BBC investigation into the case.
Elsie was attacked on October 9 1965 as she walked home through a railway tunnel near the Calder and Hebble Canal towpath.
Her body was discovered at the foot of a set of railway service steps by a dog walker at around 4.15pm.
Despite the majority of evidence gathered in the case having been destroyed, Ms Belton said the investigation is "progressing well" after new lines of inquiry were uncovered.
She added: "The force has recently increased resources for the investigation of historic cases and we are determined to do what we can to try and find justice for families, such as Elsie's, who want to see guilty parties identified and brought to justice.
"Elsie's murder may be nearly 50 years old but it is a crime people in Wakefield have never stopped talking about. I would ask anyone who can assist us."
Ian Bernard Spencer, then aged 33, was charged with the murder and cleared on the orders of the judge who heard the case at trial in 1966.
Anyone with information is asked to contact the major investigation review team on 101.