The man, 20, said: “It was a good atmosphere, it was hard dance music and everybody was having a good time vibing away.
“I wanted to remember the moment so I started filming, then I saw a lad staggering around in front of me.
“You could see him get up off the ground, everyone turned there to look. They looked a bit concerned.
“I had no idea it was Jay at first, he was proper worse for wear. He was with a couple of lads and a girl.”
After reading about Mr Slater’s disappearance, the man checked the video and saw it was the missing teenager.
“I looked back at my videos and my blood ran cold, knowing he was gone,” he said.
“All our mates [had] seen it [news of the disappearance] the next day, we were all shocked.”