The father of university chef Claudia Lawrence has urged a man who may hold vital information about his daughter's mysterious disappearance to get in touch.
A witness reported seeing a man and a woman on Melrosegate, in York, at 5.35am on March 19.
Miss Lawrence was last seen near her home in Heworth on March 18 and failed to arrive for her 6am shift at work at the University of York's Goodricke College the following day.
Solicitor Peter Lawrence, 62, said the man on Melrosegate may have a totally innocent explanation and have nothing to do with the disappearance of his daughter, but it was important for him to get in touch.
The couple were seen on a bridge near an electricity sub station on the route which Miss Lawrence normally took to walk to work.
The man was wearing dark combat trousers and was said to be skinny and was smoking a cigarette with his left hand, which has been described as "unusual". The woman was described as having mousy brown hair and wearing a blue jacket and, while police said they did not know if it was Miss Lawrence, they described it as a "significant sighting".
At his weekly news conference at his house in Slingsby, North Yorks, Mr Lawrence said: "If he gets this message and there was absolutely nothing untoward, if would be extremely helpful if we knew that.
"Somebody else must know who that is from the description; husband, partner, brother, neighbour, workmate. We really need to know, even if it is just to eliminate."
Mr Lawrence also said students returning to the city could hold vital information and he appealed to them to "search their memories".
The investigation into Miss Lawrence's disappearance is now being formally classified as one of suspected murder by North Yorkshire Police. Crimestoppers is putting up a £10,000 reward in connection with the investigation.
