He had watched Muirhead in action for many years and had often faced him across a courtroom. One of his tactics would be to seek to muddy the waters by talking up every piece of evidence, however insignificant, which tended to exculpate the accused. Any minor or trivial detail which did not point conclusively to guilt would be portrayed as if it was a fatal blow to the very heart of the Crown case.

Good evidence, from the prosecution standpoint, would have sarcasm and scorn poured upon it as if it was unworthy of even passing consideration. He recollected a particular case when he and other officers had been tipped off about a pending bank robbery. They were lying in wait when the robbers arrived and arrested two of them when they entered the premises. The getaway driver hastily abandoned his vehicle and ran off. He was a well-known Glasgow face and was identified by seven police officers at his subsequent trial when he returned from a holiday in Spain which he had arranged with an indecent degree of haste.

When addressing the jury, Muirhead had been almost contemptuous in his dismissive treatment of the police witnesses, ‘In this, the clearest case imaginable of mistaken identity based on no more than a passing glimpse of the back of an indistinct figure vanishing into the far distance...a blatant attempt by the police to turn a shadow into a figure of substance...to convert the unknown into the certain...turning an unfounded belief into a matter of certainty...such is what passes for a case against my client.’

The theory ran thus. If one policeman thought he knew who the driver was, they would all get to know who the driver was. One policeman, seven policemen, a hundred policemen, so what?

‘Ladies and gentlemen, seven officers claim to have recognised my client. That does not for a moment make it so. Imagine Ibrox Stadium on a Saturday afternoon. Rangers are on the attack. Brown sends Durie free with a perfectly weighted pass. He sprints into the opposition penalty box and is brought crashing down by the onrushing goalkeeper. The referee waves ‘play on’. The following day, you could produce forty thousand witnesses to swear blind that it was a penalty kick. It would not make it so.’

For the second time the driver got away from the police.

McAllister appreciated that, given half a chance, Muirhead was capable of doing considerable damage to an otherwise perfectly good case. The most reliable of witnesses could be made to appear as if they did not know what day of the week it was. The most honest of witnesses could be portrayed as someone you would not trust to tell you what day of the week it was.