John Leader was with his 12-year-old son Oscar as gunmen opened fire inside the Bataclan concert hall in Paris.
The pair were at the Eagles of Death Metal concert when the 46-year-old said he heard "bang, bang, bang" sounds he first thought were firecrackers on Friday night.
Mr Leader, an Australian environmental company director who has lived in Paris for the past 15 years, said that when he realised they were gunshots he pushed his son below a mixing desk. 
"The lights suddenly went on," he told London's The Daily Telegraph. "Everybody went quiet. It was clinical. All you heard was bang, bang, bang ... The shooter was standing at the back of the hall and targeting people at the front. He was taking aim. He was not spraying. It was clinical. He was aiming: aim, fire, aim, fire, aim, fire.
"Everyone was thinking 'if I move, I'm dead'."
When Oscar tried to hide under the mixing desk, an engineer waved him away as the shooters had a full view of one side of the desk.
"He tried to get up but I told him: 'Stay down, these are killers'," Mr Leader said.
He said one of the shooters was doing "crowd control" - standing with his gun at the ready but not firing and that he heard one of the assailants say something about Syria. "The other one was reloading and then he started shooting again," Mr Leader said.
"There was no way anyone was going to overpower them ... I reckon he did three or four reloads and I thought 'maybe they will just run out of ammunition'."
After a pause in the shooting - what seemed to Mr Leader like 10 to 15 minutes - someone shouted in French "they are gone".
"To my right I saw people running and saw that someone had opened an exit door," Mr Leader said. "I grabbed Oscar and said 'Let's go!'. Then we saw a lake of blood and bodies lying everywhere."
But the shooting was not over and the pair were forced to hide again. During another lull, Mr Leader pushed his son towards the exit stairs. When they got outside he could not see Oscar.
"I saw a crowd of people about 50 metres away, running," Mr Leader said. "I thought he was with them. I screamed 'Oscar' and was expecting to see him turn around but no.
"I went back to the exit and up the stairs. But by now there were bodies on the stairs, I think maybe of people who had been shot and had dragged themselves towards the exit. I couldn't see Oscar."
Mr Leader fled outside when the shooting resumed and asked a police officer down the road if he had seen his son but he had not.
In footage taken outside the Bataclan, a man can be heard desperately yelling "Oscar" as concert-goers hang from windows and drag the wounded away from the venue.
"Then I called Oscar on his mobile and he told me he was OK," Mr Leader said. "I ran to meet him. He'd lost his wallet and his shoes during our escape."
At least 129 people were killed on Friday night, with the death toll expected to rise. The attacks were at six different locations, with 89 believed killed at the Bataclan.
Footage has emerged showing concert-goers trying to flee from the theatre, with people dangling from windows and dragging the wounded away.