Police were called to an address in Holland Street at about 16:15 on Wednesday where they found the body of James Chadwick, who was from the city.
He had a number of unexplained injuries.
Following the results of a post-mortem examination, his death is now being treated as murder.
Officers have been carrying out door-to-door inquiries and reviewing CCTV images from the area.
Det Ch Insp Iain Smith, of Police Scotland, said: "This investigation is at an early stage and it is important we establish what has happened which led to James Chadwick losing his life.
"Our inquiries so far have established that Mr Chadwick was last seen on Monday 31 August and we're appealing to anyone who has any knowledge of his movements since 31 August to contact police as a matter of urgency."

Juventus face Real Madrid in Saturday's sell-out game at Cardiff's renamed National Stadium of Wales.
Grange Gardens in Grangetown was chosen for the pitch by UEFA, Cardiff council and the Football Association of Wales.
Wales legend Ian Rush praised the facility, saying it would help get more kids into football.
The 2017 UEFA Champions League final ambassador said it was important to have facilities in the inner city to give young people the "best chance possible".
He added: "Somewhere like this you go in with a positive, but where you've got muddy pitches and all that, you go in with a negative."
Rush said the next big football superstar could come from the area, adding: "We all came from places like this but unfortunately we didn't have these facilities."

The British-Brazilian duo were beaten by South Africa's Raven Klaasen and American Rajeev Ram 6-1 6-4 in an hour at the O2 Arena in London.
But Murray and Soares have already overtaken Pierre-Hugues Herbert and Nicolas Mahut in the year-end rankings.
After three round-robin match wins, they were outplayed by Klaasen and Ram.
The latter pair will play Finland's Henri Kontinen and Murray's former partner, Australian John Peers, in Sunday's final.
Kontinen and Peers beat the Bryan brothers 7-6 (7-2) 6-4 in their semi-final.
Earlier, Jamie's brother Andy Murray kept his hopes alive of ending the season as the world number one singles player by beating Milos Raonic in a thrilling semi-final, which lasted three hours and 38 minutes.
A murder investigation has been launched following the death of a 37-year-old man in Aberdeen.
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A new five-a-side pitch has been unveiled in Cardiff to create a "lasting legacy" after the Champions League Final.
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New world number one doubles team Jamie Murray and Bruno Soares suffered a disappointing defeat in the semi-finals of the ATP World Tour Finals.