In an interview with Barbara Walters he said the jury 'made a mistake'

Now, however, he says that he actually believed OJ was guilty all along

But he was declared hostile after his answers appeared to help the defense

He was called as a key witness for the

Twenty years on from OJ Simpson's 'trial of the century' a key witness who was accused of trying to help the defense says he always believed the former football star was guilty of murder.

Kato Kaelin, an aspiring actor who was living in Simpson's guest house at the time of the slayings, was called as a key prosecution witness during the now-infamous 1995 case.

He was supposed to help establish a time period when Simpson was away from his house and could have committed the killings, but his inconsistent testimony actually saw him ruled a hostile witness.

But now, in a new interview with Barbara Walters for Investigation Discovery due to air on Monday, Kaelin said he actually believed Simpson was guilty all along.

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Kato Kaelin, a key prosecution witness in the murder trial of OJ Simpson, has said in a new interview that he thinks the former sports star is guilty of killing Nicole Brown and her companion Ron Goldman in 1994

Kaelin, who was living in Simpson's guest-house on the night of the murders, was initially called as a prosecution witness in order to help establish a time when the footballer could have committed the murders

After four days of rambling and inconsistent testimony Kaelin was declared a hostile witness, and was accused by his own legal team of trying to help the defense

Speaking to Kaelin, Walters recalled hearing the verdict while standing alongside him back in 1995, and said his face appeared shocked.

Kaelin, whose real name is Brian Jerard, replied: 'I remember that because you asked me, and I said "I think they made a mistake".'

Asked whether he still believes that, Kaelin said: 'Yes, I think they did.'

Pushed on the issue further, he added: 'In my opinion, yes I think he is guilty. In hindsight I think that OJ Simpson is guilty.'

Nicole Brown, the former wife of OJ Simpson, was found dead outside her home in Brentwood, Los Angeles, in June 1994 alongside Ron Goldman, an aspiring actor, model, and her close companion.

Investigators said Simpson went to Nicole's condo, stabbed her and Goldman in a fit of jealous rage, then left on a flight to Chicago later that night, disposing of evidence along the way.

Kaelin had been with Simpson on the night of the murders, and had been one of the last to see him just before the time police said Nicole and Goldman were stabbed.

According to Kaelin's testimony at the time, he and Simpson had gone to get McDonald's drive-thru at around 9.30pm, returning to his house shortly afterwards.

Kaelin said he then went to the guest house to eat, and didn't see Simpson again until 11pm, when a limo arrived to take him to the airport.

It was during this time window that prosecutors alleged Simpson went to kill Nicole and Goldman.

In a new interview with Barbara Walters, Kaelin says he was only trying to tell the truth of what he knew, and actually believed Simpson was a murderer all along

Kaelin recalled how he watched Simpson's 'not guilty' verdict alongside Walters, and whispered in her ear that the jury 'had made a mistake'. OJ is pictured during his trial in 1995

Once Simpson arrived back at the house, Kaelin said he helped the former sports star pack his bags into the car before he left.

Recalling the events of that evening now, Kaelin said: 'I was helping to pack stuff into the limo because he [Simpson] was going to Chicago.

'There was this bag that was ready to be packed and he [Simpson] said "don't touch that", and that bag was never found.'

Asked by Walters whether he now thinks that bag contained the murder weapon, Kaelin added: 'I don't know what was in there, but something enough for OJ to say "don't touch that".'

Prompted on his now-famous testimony during the trial, Kaelin said: 'I could only say what I knew, and that is what I testified to.'

Simpson was ultimately acquitted in the murder case, but later found liable in the deaths of Nicole and Ron in a civil lawsuit brought by their families.

O.J. was later convicted and sentenced to 33 years in a Nevada case involving the theft of his own sports memorabilia.

Two decades after the trial of the century, a true crime anthology TV series about it is currently in the works.

American Crime Story will air next year, and sees Cuba Gooding, Jr. as O.J., while John Travolta plays his famous attorney Robert Shapiro.

Ron Goldman (left) and Simpson's former wife Nicole Brown (right, with Simpson) were found stabbed to death outside her LA condo in 1994

David Schwimmer will portray Robert Kardashian, and has been talking to Kris Jenner to get tips on how to play the lawyer.

Jenner, who was married to Kardashian until their divorce in 1991, knew both Simpson and Brown well during their marriage and relationship.

In previous interviews, Jenner said: 'At the end of Nicole's life, I think she finally was at a place where she knew she had to be more vocal with what was going on and she was in trouble.

'The one thing she would tell all of us by the time, you know, it got to that level was, “He's going to kill me and he's going to get away with it.'

Kris didn’t take the threats too seriously, and she admits she feels guilty about not doing more to try and help her friend.

‘I will always feel guilty that I didn't pay more attention and didn't speak up when I thought anything was wrong or asked her more, “Do you want to talk about it?”’ the reality star shared.