Canadian detectives investigating a 32-year-old cold case are trying to trace a woman who lived in York.
Officers want to make contact with Lillian Crook, whose brother Dennis Crook was reported missing back in October 1985.
Mr Crook was 34 years old when was reported missing by friends on October 22 and had not been seen since for six days beforehand.
The investigation team, based in Victoria, said that it was conducting an international missing persons search in an effort to locate Mr Crook and wanted to find his sister as part of their inquiries.
Mr Crook was born in England and completed his further education studies in York, before going on to graduate from the University of Nottingham with a bachelor of arts degree.
He was living in Victoria, the capital of British Columbia, when he disappeared.
In an appeal shared by North Yorkshire Police, the investigation team said: "Lillian Crook, Dennis’ sister, is known to have resided in Holgate, York. Investigators are looking to find Lillian and speak with her.
"Our officers are reaching out to the North Yorkshire Police, as well as residents of Holgate as part of our efforts to locate Lillian and ultimately, Dennis.
"Investigators are also looking to speak with Dennis Crook’s friends here in Victoria, including those who initially reported his disappearance, or those who knew Dennis."
Mr Crook, now a 66-year old, is described as white, 5ft 9in, with a medium to large build.
There are no known photographs of Mr Crook at the time he went missing, but he had brown eyes and black hair.
Anyone who knows Lillian Crook is asked to email Chantal.Ziegler@vicpd.ca with information.