A previously-unseen witness statement has cast doubt on the investigation into Brian Jones' death.

The Rolling Stones musician was found dead in his swimming pool in 1969 aged 27, with a coroner recording a death by misadventure, saying he had drowned while "under the influence of alcohol and drugs", but the family of cab driver Joan Fitzsimons - who had been at the guitarist's house on the night he passed away - told cops they were convinced she had been attacked days later because of her belief then-boyfriend Frank Thorogood, a bodyguard to the star, had been involved in the tragedy.

Three weeks after Brian died, Joan was found unconscious in the back of her car, blinded in both eyes, with a fractured skull and three front teeth missing, and her brother John Russell told police investigating the attack that she was "frightened" of Frank and believed there was more to Brian's death than the official verdict.

The statement - which was placed inside the National Archives with an order it remain closed until 2014 - has been released under a Freedom of Information request and in it, John recounted a conversation he had had with his sister just days before she was attacked.

According to the Sunday Telegraph newspaper, he said: “She said that she was frightened of Frank and she started talking about the death of Brian Jones.

“She had been over at his house that night just before he died and she thought that he [Jones] was quite able to look after himself.

“She said that things hadn’t finished there yet and if it got out that she thought this, then she would be the next one.”

John said Joan planned to go to the press about Brian's death.

He added: “We then went on and talked about it and I told her to be careful.”

The siblings' mother, Irene Russell, told cops Frank had turned up at the family home days before the attack demanding to know where her daughter was.

She said: “Frank said to me that Joan knows a lot about the Rolling Stones that shouldn’t get out. Joan, as it appeared to me, was frightened of Frank.”

While newspaper reports at the time linked the attack to Brian's death, Sussex Police insisted there was "no truth" in the claims, but according to evidence released in the Freedom of Information request, cops actively worked to "eliminate" the lines of enquiry.

A letter from the Sussex chief constable’s office in 1969 regarding Joan said: “She is to be asked as to her reason for allegedly being afraid of Mr Francis Thorogood as referred to in a statement of her brother Mr John Russell and what knowledge she has relating to the death of Brian Jones which causes her to be frightened.”

And in 1994, Albert Evans - the junior policeman who was first on the scene - described the investigation into the rocker's death as "most unsatisfactory" and was convinced Frank was involved somehow.

He wrote to the Chief Constable: “I personally was not convinced that we were given the correct story by Thorogood and his associates.”

While he believed the minder was involved, he claimed when two senior officers arrived hours later, the number of witnesses was reduced from more than 20 to just Frank, Brian's girlriend Anna Wohlin, and a nurse named Janet Lawson, but the probe was focused on drugs and alcohol.

Years later, both women said they hadn't written their own witness statements.

Janet told the Daily Mail newspaper in 2008: “The policeman suggested most of what I said. It was a load of rubbish...

“I went into the house to look for Brian’s inhaler. Frank jumped back in the pool, did something to Brian and by the time I came back, Brian was lying peacefully on the bottom of the pool with not a ripple in the water.”

Frank was eliminated as a suspect in the attack on Joan after his wife said he had been in London at the time, and he was never charged with any offences. He died in 1993.

Sussex Police insisted they have no plans to reopen the investigation into Brian's death.

A spokesperson said: “The death of Brian Jones was investigated in 1969 and was also the subject of two reviews initiated by Sussex Police, in 1984 and 1994.

“No new evidence has emerged to suggest that the coroner’s original verdict of ‘death by misadventure’ was incorrect. The case has not been re-opened and there are no plans for that to happen.”