Fergus McInnes was last known to have boarded a flight at Edinburgh Airport to Geneva where he was to attend a conference last Tuesday. He works at the Centre for Speech Technology and Research at Edinburgh University.
Fergus, who is 51, did not check into his hotel in Switzerland.
"Mr McInnes’ sister, Lorna, 41, was visited by her brother at her home in Blairgowrie, Perthshire, two days before he took the flight.More details here.
She said: “There was no sign he was going to do anything like this. He seemed very upbeat. It is very worrying not knowing and just having to wait for answers. The police have been very good at keeping us informed.”