He was 34 years old at the time and had been working for UNIDO in Vienna. Two eyewitness reported seeing him running naked from a gay sauna – the Kaiserbrundl – after reportedly being assaulted, although his last confirmed location was a sauna on Stephansplatz after work.

At the time police said that he was HIV positive and suicidal and that he jumped into the Danube and drowned – something his mother has said she finds hard to believe as he was very happy and had recently had an HIV test which showed he was negative.

She believes the Vienna police botched their preliminary investigation into her son’s disappearance, and then covered up their mistakes.

Initial police accounts said that a fisherman later saw a man floating face down in the river and that the department responded with divers, but did not recover a body.

This week, ten divers from the Cobra Team used specialized equipment including sonar, and searched the canal from Freudenau until Urania.

Mario Hejl, a spokesman for the Federal Criminal Investigation unit, said that the canal had been closed to ships and although the diving operation was dangerous Cobra had tried to keep risk to a minimum.

Hejl said that the likelihood of finding skeletal remains after eight years is slim, and believes that they could have become trapped in the canal’s groynes – concrete and steel structures which improve navigation and prevent erosion.

According to Joseph Gepp, an investigative journalist with Profil magazine, detectives have not given up on the case and are continuing to follow up leads and interview people.

Each year since 2008, Gillern's mother has held a vigil on October 29 outside the Kaiserbrundl to commemorate the disappearance of her son.

Aeryn Gillern’s disappearance is the subject of an award winning documentary film, called Gone.