It was merciful. Lord Cullen's inquiry into the killings at Dunblane was close enough to the daily finishing time that Colin Campbell QC was able to say he would continue questioning the witness in the morning.

Campbell, representing the families of the 16 children murdered by Thomas Hamilton, had seen that the senior police officer he had been grilling for the last three hours was on the verge of breaking down.

Douglas McMurdo, former deputy chief constable of Central Police, had arrived at the inquiry in Albert Halls, Stirling , on Thursday morning.  About 10 minutes before he took the stand he met with the force's solicitor, James Taylor, and was shown where he would be sitting while giving evidence and from where the questions would be fired.

As the senior police officer who signed Hamilton 's firearms certificates in 1989 and 1995 and corresponded at length with him over his various complaints against the force, it was clear McMurdo was going to be giving evidence for some time.

That realisation led Lord Cullen to agree to the concession of a mid-morning break adjournment to give the witness a break, the first time in 12 days of evidence there had been any change to the routine.

It was at the end of almost five hours in the witness chair on Thursday that McMurdo, 55, now promoted to the post of assistant to Her Majesty's Chief Inspector of Constabulary, broke down in the most open display of emotion by any of the 100-plus witnesses who have so far given evidence.

There had been no real clue of what was to come.  He had coped confidently with some tough questions put by the Crown's senior counsel, Iain Bonomy QC .

There had been raised voices in the rapid exchanges between the two and the occasional indignant yes or no answer, but silver-haired McMurdo, leaning slightly forward on the elbows of his dark-coloured suit, had appeared in control.

Then at 12.39pm Campbell took over and as the afternoon wore on the questions began to get more personal: "You were the officer ultimately responsible for issuing Hamilton's firearms certificate?" and "Since the awful tragedy have you gone over events [leading up to granting Hamilton's certificate] in your own mind?" to which McMurdo replied: "It's never been out [of my mind]."

Campbell unnerves witnesses.  After asking questions, the QC avoids eye contact with the subjects of his interrogation preferring instead to look at papers, whisper with colleague Laura Dunlop QC or pour himself a glass of mineral water.

But when McMurdo, 55, faltered just after 4.15pm, Campbell's eyes flicked back to him.  The QC had asked a rambling question about whether people spending their leisure time using guns outweighed the risks of such weapons being readily available.  Choking on his answer, McMurdo turned to face Campbell, his head slumped down towards the floor and he pushed his spectacles back up over his eyes where tears were forming. Catching himself, he said: "I'm sorry," before blurting out almost inaudibly: "I think we could ban them [ guns ] before suffering another tragedy like this."

Granted an early release by Campbell, McMurdo found his composure again within seconds, leaping to his feet, smiling and laughing with colleagues.LINK

He even remembered to thank the man who held open the passenger door of the white Vauxhall Vectra which whisked him away from the Albert Halls a few minutes later with a screech of tyres to outpace the television cameraman running alongside.  McMurdo was back to complete his evidence on Friday but there was nothing approaching the tension and drama of the previous day.

The third week of the inquiry had been largely taken up with police officers involved with Hamilton's applications for firearms certificates, from the beat officer who went through the form with him to McMurdo who signed the documents.

McMurdo told the inquiry he knew as much about Hamilton as any officer.  He was involved in dealing with the complaints Hamilton made about police investigations into his boys' camps.  He met him only once.  Like many others, he became embroiled in long-running correspondence with Hamilton about grievances and also received copies of letters he sent to local MP Michael Forsyth.LINK

The tedious nature of the relationship taking up so much of his time finally exploded in 1992 when McMurdo fired off an angry letter to the Scottish Office.  In the letter dated January 14, McMurdo wrote: " Hamilton is a bitter and petty-minded individual and over almost four years I have received his ever more emotional outpourings.  Like dealing with a zealot, he re-introduces points again and again and I can see his correspondence continuing indefinitely.  This is something I am not prepared to do."

At the inquiry last week, McMurdo admitted he had "lost his cool" when he wrote the letter but none of his knowledge of Hamilton was enough to prevent his firearms certificate being renewed just a few months later.

"Everthing I knew about him was related to boys' camps.  There was no evidence he would be dangerous with a firearm," McMurdo said.  When Hamilton's firearms certificate was last renewed in 1995, McMurdo said he only spent a few minutes looking over the application before signing it.

This week the inquiry will examine Hamilton's contacts with local authorities.