'John explained that if they (the IRA) began firing, then it would justify the Paras' decision to fire on unarmed civilians'
Creggan-raised Gerry (68) lived with his family in Fanad Drive. He was an 18-year-old pupil at St Columb's College at the time and was studying for his A-levels that day.
Gerry decided to take some time out to go for a walk and to see what was happening in the city centre.
His father - a former British soldier who had been a prisoner of war during World War II - warned his son to stay away from a civil rights march scheduled to take place later that afternoon.
Mr Murray said he didn't like the attitude of the soldiers during a confrontation with John Hume and other civil rights activists on Magilligan Strand the previous week.
And as two young police officers had been shot dead by the IRA near St Eugene's Cathedral a few days before, he expected trouble.
"Stay away from it," Mr Murray told his teenage son.
The march was more or less over by the time Gerry neared the top of William Street. He could see minor rioting in the distance. And as he walked on, he sensed tension in the air.
"The soldiers appeared to be very serious and aggressive. It was a bad atmosphere. It was menacing," he said this week.
Gerry also remembered his dad's words of warning and around 4.15pm, he decided to turn back and head home.
It was then he heard the first shots. The sound of the soldiers' rifles was louder and sharper than normal. "I knew they were high-velocity rounds.
"The shooting didn't last long, but it was high-intensity firing. It was a lot, in fact an awful lot of shots. I knew in my heart people must have been hit.
"I walked across the road and came to a place known as 'the iron steps'.
"A car load of men appeared from nowhere and I could see they had rifles and other guns with them.
"I knew they were the Official IRA - the Stickies - and it seemed they were determined to get involved in an exchange with the Paras. But suddenly John Hume - who lived nearby - appeared on the scene. I knew John because he'd taught me at school.
"John pleaded with them to go away and to take their guns with them. In fact, he insisted.
"John explained that if they began firing, then it would justify the Paras' decision to fire on unarmed civilians.
"I could hear what they were saying and the IRA men were determined to make some kind of stance, because the Army had killed innocent people.
"But in the end, they listened to sense.
"John persuaded them it was wrong and they got back into the car and left," said Gerry. He added: "I honestly believe that if it hadn't been for the actions of John Hume that day, then the death toll could have been a lot higher."
On arriving back in Fanad Drive, Gerry met his father.
"He was ashen-faced. The death toll was growing by the minute. My father told us that when the firing started he'd taken refuge in a shop doorway along with Barney McGuigan.
"My father said he told Barney to keep his head down, but Barney believed that on account of his age - he was 41 and clearly not a teenager - he'd be alright.
"Barney stood up and pulled out a white hankie, but a Para blew his head off," said Gerry.
He added: "My father witnessed that." Now a successful accountant and writer, Gerry Murray has no doubt about his abiding memory of the events of Bloody Sunday.
"For me, it was the sight of 13 coffins in St Mary's Church in the centre of Creggan. I knew most of these people to speak to.
"I had been at school with some of them.
"But until the day I die, the memory of the 13 coffins will remain with me," he said.