But this week Det Supt Gough of Northern Constabulary is an unhappy man. "I'm extremely frustrated, baffled. Barring some kind of miracle, we are going nowhere," he says. For Mr Gough, a plain-speaking, stocky Highlander, this week marks one anniversary he would rather forget.
It is one year since Orkney suffered its first murder for a quarter of a century. At 7.15pm on 2 June last year, a man wearing a balaclava and gloves strode in to the Mumutaz restaurant in Kirkwall, the islands' capital. He pulled out a pistol and shot a waiter, Shaymol Mahmood, at point-blank range.
The bullet passed straight through Shaymol's head and lodged in the wall next to a table where a local family was eating the chef's special.
As the 26-year-old collapsed and died, the gunman walked out of the restaurant and ran down a narrow alley. He was last spotted near Kirkwall pier.
As Det Supt Gough sailed from John o'Groats to Orkney late that night, he was confident the murder would be solved within weeks. After all, the killers of crofter Andrew Bruce, the last islander to be murdered, in 1969, were arrested before breakfast the next day. "Orkney has a village mentality; this is a village crime. People there say you can't pee in the dark without someone seeing you. We'll get something soon," he told himself.
It was months before he left Orkney and returned to force headquarters in Inverness - empty-handed. Some 4,000 people had been interviewed, including tourists from as far away as Japan and Australia. Every home in Kirkwall was visited and waiters at scores of Indian restaurants in the Highlands had been questioned. But all inquiries were in vain. The hooded gunman had, it seemed, disappeared into the Orcadian night.
Det Supt Gough and other detectives have returned to Orkney a dozen times in the past eight months but the case is still as impenetrable as ever.
"Whenever we go to Orkney, we look at all theories," he said. "We thought there could be a racist motive, but we have now ruled that out.
"We have considered some kind of feud within the Bangladeshi community but there is no evidence of that. We looked at mistaken identity but dropped it. There was no attempt to rob the place. And, clearly, the killing was not some kind of impulsive crime.
"We have worked with other forces and Interpol and found no family feuds, no jealous husbands and no debts. I have been involved in a dozen murders in my 20 years in the Highlands and this is by far the most baffling. We just cannot find a motive or any positive leads."
Shaymol, from a respectable Bangladeshi family, was a hard-working, popular waiter at Kirkwall's only curry house. In broken English, the owner of the Mumutaz, Moina Miah, 36, who came to Orkney from Aberdeen three years ago, says he cannot imagine why anyone would want to kill him: "He was a very good worker - all the time smiling. Customers liked him. Sometimes there were arguments with people who were drunk who wanted to come in. But nothing serious. I am still shocked. I run a good business. I cannot think why this happened here."
Mr Miah, who fears that the gunman may return, has put his restaurant up for sale. Although the bullet hole has been papered over and a new carpet fitted, he has received no offers.
The killing still shocks the local Kirkwall community where, for the first time in a generation, people have begun to lock their doors at night.
The Rev Ron Ferguson, the local Church of Scotland minister, said: "People talk about that dreadful night. There is unease and a great sense of bewilderment that it could have happened here.
"Most think it was a contract-style killing, revenge for something that happened when Shaymol was working in England or Bangladesh. But there are those who have genuine fears that the killer is still here on Orkney and may strike again."
It is a fear shared by Det Supt Gough. After the murder, airports and ports were sealed off and there were no sightings of small vessels leaving any of the islands' secluded bays. "My experience tells me the murderer is more likely to be local than an outsider, still there in the community," he said.
But he is no more confident of finding him now than he was a year ago. After one last appeal for information later this week, the pounds 200,000 police investigation on Orkney will officially be scaled down.
Detectives don't like to admit it, but most now think that a far-flung outpost of Britain's tandoori empire has witnessed the perfect murder.