Footsteps approached his office and he turned to see Joe Johnstone striding towards him carrying a file. Johnstone was head of the firearms section. A former army weapons instructor, he had spent his life studying guns and the science of ballistics. What he didn’t know about the subject could be inscribed on the head of a pin. Given any encouragement, he would talk guns till the cows came home. He had the habit of using ten words when one would have sufficed. Joe Johnstone was a man who could bore for his country.

‘Well, Joe?’

‘I thought I’d bring this over personally. Too important to entrust to one of the underlings. I knew you would be anxious for the results and I didn’t want to keep you waiting. Time can be of the essence in these cases. You’ll want to catch the bird before he flies the nest, I dare say. I thought you’d prefer to see the results rather than just a telephone call. No room for misunderstanding when you see it in print. Sometimes, down the phone, people can get the wrong end of the stick. Too desperate to hear what they want to hear, that sort of thing. I take it this is fairly important?’

‘Joe – what is the bloody result?’

‘Here. Read it for yourself.’

McAllister took the report and began to study it with the utmost care.

The first three pages described the comparison test which had been carried out involving the bullets and cartridge cases from the Boyle killing and test firings from the weapon recovered at Stranraer. The barrel of a gun imparts distinctive marks to a bullet as it passes down its length. Each barrel is unique. When cartridges are ejected from a self-loading pistol the metal of the gun will leave equally distinctive striation marks on the metal of the case. These are as unique as fingerprints and enable experts to establish if a particular bullet or cartridge was fired by or ejected from a particular weapon. He turned the page and studied the conclusion.

‘The bullet fragment recovered from the head of the deceased was nine millimetre and of typical fired appearance. It had been significantly damaged by contact with a hard surface and was unsuitable for comparison purposes.’

‘Damn!’

‘Read the first paragraph, eh? Don’t worry, it gets better.’

‘The cartridge cases from the test firings of the Browning pistol were compared with the cartridge cases found at the Boyle locus. The striation marks on the cases caused by ejection from the weapon were examined under a comparison microscope. In our opinion they were identical and we have no doubt that the cartridge cases found at the Boyle locus were fired from the Browning pistol found at Stranraer.’

‘Got him!’

‘I told you it got better. I always believe in saving the best for the last. Keeps people interested. Builds up the tension.’

‘Thank you, Joe. Is there any doubt?’