Police have revealed that the man last seen with a missing Polish woman in Glasgow was a registered sex offender.
Angelika Kluk's disappearance has mystified her friends and family
A man previously thought to be Patrick McLaughlin has now been identified as 60-year-old Peter Tobin.
Angelika Kluk, a 23-year-old student, was reported missing on Monday after she failed to turn up for work.
Police had released a picture of Mr Tobin, who was believed to be living rough in Glasgow. He met Angelika at some time on Sunday afternoon.
Mr Tobin had been doing odd jobs in the city's St Patrick's Church for the past six weeks and he told everyone there that his name was Pat McLaughlin.
Strathclyde Police said that it was now believed that he was in fact Peter Tobin, with a last known address in the Paisley area.
Mr Tobin was considered a potential risk to members of the public.
Chief Inspector Elaine Ferguson, officer in charge of the investigation into the whereabouts of Ms Kluk, said: "This new information that has come to light, as a direct result of media coverage, is of considerable importance.
"I would stress, however, that everything possible is being done to trace Angelika and we have no information at this time to suggest that she is with Mr Tobin.
"However, we have to pursue every line of enquiry and cannot discount this possibility. It is known that Angelika was in Mr Tobin's company on Sunday afternoon, the day she was reported missing."
She added: "I would appeal for the public's continued support and would ask that any sightings of either Angelika or Peter Tobin be reported to the police immediately."
The Roman Catholic Archdiocese of Glasgow issued a statement saying fears were rapidly growing for Angelika's safety.
Ronnie Convery, the archdiocese's spokesman, said: "This is shattering news and clearly alarming. Our fears are growing for Angelika.
"All we can do is hope against hope and pray that Angelika is found safe and well."
Anyone who sees Mr Tobin has been advised not to approach him but to notify Anderston Police Office on 0141 532 3262 or their nearest police office.