At a press conference this afternoon, Strathclyde Police Divisional Commander John Thomson explained Stuart suffered a "violent and sustained" attack in the early hours of Saturday morning.
Officers are still keen to piece together Stuart's movements between 2.30 and 4.50am prior to the discovery of his battered body at Caponacre Industrial Estate.
He last spoke to a family member outside Cumnock Fire Station at 2.30am.
Divisional Commander Thomson said: "We don't believe this was a random attack.
"We remain optimistic that we will bring an individual or individuals to responsible to book sooner rather than later.
"Stuart was at a number of parties in the area before 2.30am and we are looking at the possibility he knew the people involved."