On March 13, 1996, a gunman shot dead 16 children and their teacher at Dunblane Primary School in Stirlingshire. It was a crime that shocked Britain and the wider world for its depravity and senselessness. In the wake of the murders, MPs passed some of the most sweeping firearms legislation in any jurisdiction, including a ban on private handgun ownership, and measures were taken to tighten security at schools.

Ahead of the 20th anniversary, STV's John MacKay, one of the first reporters on the scene, recalls the events of that day and reflects on efforts to ensure they could never be repeated.

'Then there was silence. The shooting and the screaming had stopped.'

That devastating sentence, spoken in a packed but hushed public hall, remains the most compelling testimony I have ever heard.

Sixteen infant children and their teacher had been killed by a gunman in their gymnasium at school. That much we all knew.

The fact of it was awful enough. It was the detail that ripped the heart.

We were all hearing that detail for the first time from a smartly dressed woman speaking calmly and without emotion. This was how it had been. We knew that because the woman telling us was there. Eileen Harrild had been the gym teacher. She had seen it happen and had been shot herself. She bore witness in the impact of her words and the visible wounds on her arm.

She described how the infants had lined up excitedly in their gym clothes ahead of the class. The contrast between that image and devastating silence could have been no more than ten minutes.

STV reporter Dougie McGuire was one of the first on the scene. He remembers the awful moment of confirmation clearly:

I can still picture the inside of the car, my tweed jacket sleeve and the notepad on my knee when the girl on the phone from ambulance control said the most devastating words.

"Ambulance are in attendance at Dunblane Primary School. There are sixteen children dead and two adults."

"Sorry, did you say 16 children?"

"Yes, it's awful."

That disbelief was the widespread reaction. This was Scotland. Children did not get shot in school in Scotland.

I shared that bewilderment travelling north with a page of news agency copy in my hand. The moment of confirmation was when my cameraman Mike Haggerty undertook a police car and it didn't react. What awfulness lay ahead of us? We arrived, grabbed our gear and ran up to the school amid desperate parents not knowing what had happened to their children.

The other surviving adult from the gym, Mary Blake, was still recovering from her injuries. She couldn't attend the inquiry in person, but in her written statement she described trying to protect the children hiding in a storeroom, one wee soul saying over and over, "What a bad man. What a bad man."

Harrowing detail piled upon harrowing detail.

A doctor describing moving from victim to victim checking who could be saved and who was dead.

A senior policeman saying how difficult it had been to identify some of the victims. The label on one child's clothes didn't match any name on the register. The one person who knew them all so well, their teacher Gwen Mayor, was herself dead.

The janitor telling the deputy head: "You can't help them, Miss; they're gone."

The day after the shootings a package was delivered to STV (and other media outlets), just a brown A4 envelope with the address hand written in small, untidy letters. It contained copies of letters sent by the killer Thomas Hamilton to the Queen, the Scottish Secretary and the local MP charting a growing grievance about how his work with children was being undermined. It was chilling to realise suddenly that he had sent them himself.

He had posted them the previous day. It could only have been when he was on his way to Dunblane.

The inquiry heard that Hamilton had questioned a boy in one of his clubs about the layout of the school and the time of the assembly. The boy got the time wrong and in that one mistake possibly saved many more children. When Hamilton arrived that awful morning, he cut the phone wires and carried enough ammunition to kill almost every child in the school.

This was no rampage by a man out of his mind. This was a planned slaughter of young children.

Above us in the hall, in a balcony closed off to the media and public, the unseen parents of the victims sat listening to the same testimony. What must they have endured?

We couldn't know because there was an understanding that the families were to be left alone and they were.

The day before the inquiry was to end, they faced the cameras for the first time. Regular folk like you would see in any town in Scotland. Of course they were. What else were they going to be? This could have happened in any town in Scotland.

They had one clear message - the right their children had to life far outweighed anyone's right to own a gun.

Any time I go to a school now and I have to press the buzzer for entry I think of these wee kids at Dunblane.

Some will say the security we have in schools now and the ban on handguns mean the children did not die in vain. It can never happen again. There is always an understandable need to make some sense of tragedy, to seek a handhold that allows us to pull away from the blackness and move forward.

I'm not so sure.

These children died because an evil man, rotten to his soul, decided that if children were to be denied to him, they would be denied to their families.

It was as evil and pointless as that.

John MacKay is the presenter of the STV News at Six and Scotland Tonight. His 30 years in journalism are chronicled in the book Notes of a Newsman.