Speaking from the Heights Bar in Loughinisland, where loyalist gunmen carried out the murders, Kevin Gordon said what he found "never leaves you".
On Thursday, an official report said there was collusion between police and loyalist gunmen in the killings.
"Everybody knew in their hearts there was a cover-up," Mr Gordon said.
"For it to be exposed at such a high level is a relief."
An emotional Mr Gordon told the BBC: "Talking to the relatives, there's that sense of justice being done and their long campaign has been justified."
The Catholic victims were in the bar watching the Republic of Ireland play a World Cup football match against Italy on 18 June that year, when two Ulster Volunteer Force (UVF) members walked in and opened fire indiscriminately.
They were killed instantly.
Mr Gordon said he was driving past the bar on what was "a beautiful summer evening" and saw a friend come "staggering out of the bar".
"I thought he perhaps had too much to drink but he wagged me down," he said.
"I stopped and he said: 'Kevin, Kevin, help us, they've shot us. There's six dead in here.'
"I abandoned my car outside the door, I came in and the bodies were lying.
"I was in for a long, long time - it seemed a long time. Obviously, you're in shock and as time lapses, you don't realise how fast it goes."
Mr Gordon said that he felt comfort in returning to the bar after the attack, and that he and others found it to be "a good place to meet".
But he added that he is still dealing with the trauma of what he witnessed that night.
"I actually found solace in meeting my friends and we talked about it, a shoulder to lean on, rather than sitting at home," he said.
"Of course you remember, you never forget - I personally am still getting treatment for it.
"Twenty-two years down the line and it'll never ever leave you.
"You walk through this room and you look at that plaque on the wall and you remember your friends - I knew every one of them.
"I'm delighted, if that's the word, that the families, who have fought a really hard, emotional battle for 22 years, have got justice at last."
The first person to arrive at the scene of the massacre of six men in a County Down pub in 1994 has said he is still having counselling after what he saw.