Officer 1483, John Sutherland was quite often in McLevy’s team of officers when making arrests.
He joined the Edinburgh police on 20 January 1853 aged 25. He was single and previously had been a labourer. The popularly believed master of Greyfriars Bobby, John Gray, also joined a few days later. John Sutherland was shorter than McLevy at 5 foot 8 inches, with grey eyes, brown hair and an oval face.
He resigned in February 1857 as many officers were want to do. Drinking on duty was something that many officers did and were disciplined for although it is unknown why John Sutherland resigned.
James McLevy 
There’s no evidence that P.C. John Gray was connected with Greyfriars Bobby. Eleanor Atkinson named her character Jock Gray in her novel published in 1912 which led to the belief that the owner’s first name was John. P.C. John Gray is buried in Greyfriars Kirkyard. Although a memorial stone to Auld Jock was set up in the kirkyard in 1925, the farm labourer only existed in Eleanor Atkinson’s novel.
I agree and have changed the text accordingly. PC John Gray did exist and the evidence for that connection comes from the research book on Greyfriars Bobby by Forbes MacGregor. The page on John Gray says more.