Suzanne Pilley was attacked after reaching her office, murder detectives say

• Police now believe Suzanne Pilley, 38, has been murdered. Picture: PA

Detectives believe that Ms Pilley did make it to her work on the day she disappeared.

However, there is mystery over what happened to her after arriving at her office, where fellow workers reported her absence after she failed to appear at her desk.

Her office at Infrastructure Managers, on Thistle Street in Edinburgh's New Town, is on the second floor of the building. Her colleagues are now expected to be re-interviewed by detectives, who previously believed she had not arrived there.

Sources insist the police still do not know whether or not she made it inside the building.

The police say they have upgraded their missing persons inquiry into a murder investigation after establishing Ms Pilley made her normal way to work and there is "no proof of life".

However, it is thought other crucial evidence secured in the last couple of days has convinced the police she has been the victim of foul play.

In a statement, her parents Robert and Sylvia said: "As a family, we still live in hope of good news, and would still appeal for people up and down the country to stay vigilant and look out for Suzanne.

"We have, however, been kept informed of the way the inquiry has been progressing, and deep down we do suspect something more sinister has happened. Suzanne would never put us through this kind of worry intentionally, so we can't help but think she has come to some harm."

Forensic officers have already carried out extensive searches of properties in Thistle Street, where her office is located, including several garages.

The first appeal over Ms Pilley, 38 – last seen shortly before 9am on 4 May – was issued two days later, but it was on 11 May that detectives said they were "gravely concerned" for her safety.

Ms Pilley's colleagues at Infrastructure Managers have already been quizzed to help police build up a picture of her normal routines and possible reasons for her disappearance.

Detective Superintendent Stuart Houston said: "Our investigation has led us to believe that Suzanne has been murdered. The CCTV image we found shows her yards from her office door. We can't be sure at what point any incident may have taken place. The image itself is unclear and we are working on it to see if we can get any more information from it. We have more footage to go through.

"We are following a number of lines of inquiry. Officers have been speaking to employees at her place of work as part of the investigation. We're still keen to explore all possibilities."

Ms Pilley, who left home in Stonehouse shortly before 8:20am on 4 May, exchanged text messages with her parents before departing a No 4 Lothian bus on Princes Street, near the Jenners store, at 8:48am.

She then made a brief visit to Sainsbury's, on St Andrew Square, and is captured on camera at the corner of nearby North St David Street and Thistle Street, and also outside her office on Thistle Street.

The capturing of the last image was described as "hugely significant".

Detective Chief Inspector Gary Flannigan said: "We are satisfied through the clothing, its colour and the timescale in which the image was recorded that it is Suzanne.

"It further proves this was a routine morning for Suzanne, and she was following her usual patterns – we suspect she may well have made it to her office as normal."

A spokesman for Infrastructure Managers said: "We were informed this morning by the police that they are now treating Suzanne's disappearance as a murder investigation.

"We'll continue to co-operate fully with the police in every way possible and hope that anyone with any further information about Suzanne's disappearance will come forward."