The Daily Mail reports that the singer, who separated from Hullis after 12 years of marriage, was investigated by the US authorities following allegations that he made numerous death threats to his wife’s London-based lawyers.
The documents, which were released last week in the US by the FBI under Freedom of Information laws, reportedly show just how ugly the split turned.
Robin Gibb of the Bee Gees at his wedding to Molly Hullis in 1968
In a telegram to solicitors Haymon & Walters in March 1981, the newspaper reports he claimed he had hired a hitman. "I warned and warned you," he cabled. "The situation is now very serious.
"Know [sic] one walks all over me . . . I have had enough. I have taken out a contract. It is now a question of time."
Last month it was reported Gibb, who died from cancer in May, refused to visit doctors for scans that could have detected his illness because he wanted to go on a world tour.
Gibb, 62, died after a long battle with colon and liver cancer.
His widow Dwina Gibb, 59, told the Daily Mail Weekend magazine that the music star initially ignored her pleas and doctors' advice to have the cancerous cells fully checked.
The Bee Gees' song catalogue, which includes Massachusetts, I've Gotta Get A Message To You, Lonely Days, How Can You Mend A Broken Heart, How Deep Is Your Love and Stayin' Alive, led to their induction into both the Rock and Roll Hall of Fame and the Songwriters Hall of Fame.
Gibb's twin brother Maurice died of a heart attack in 2003 following intestinal surgery and Gibb's younger brother Andy, who was not part of the Bee Gees but a successful singer in his own right, died in 1988 from heart failure aged 30.
Andy Gibb eats a cherry from his birthday cake at a party given by his family in his home in Miami Beach, Fla., Monday night, March 6, 1979. Andy's brothers, the Bee Gees, from left are, Robin, Barry and Maurice. (AP Photo)
The Bee Gees, from left, Robin, Barry and Maurice Gibb, attend a party in 1978
Members of the Bee Gees pose with Barry Manilow, far right, at the American Music Awards in Los Angeles, Ca., Friday, Jan. 13, 1979. The brothers Gibb, from left, Barry, Maurice, and Robin, won awards for favorite popular group and favorite soul album
The Gibb brothers: Barry (centre) and twins Maurice (left) and Robin (right)
The Bee Gees (L-R) Barry, Maurice, Robin Gibb at Heathrow Airport, London, before leaving for a 3 month World Tour. 1974
The Bee Gees, (l to r) Robin, Barry and Maurice Gibb, accept the Brit Award for Outstanding Contribution in 1997
Bee Gees Singer Robin Gibb reads to his son Spencer, circa 1974
Bee Gees Singer Robin Gibb with his wife Molly Hullis (r) and two children Spencer and Melissa in his home, circa 1974
Robin Gibb, founding member of the Bee Gees, unveils a plaque honouring the work of the Bee Gees at 67 Brook Street, central London. 2008
Robin Gibb performs at the BBC Electric Proms 2008 - Saturday Night Fever at the Roundhouse, Chalk Farm, London.
Official ambassador Robin Gibb CBE (centre) with his wife Dwina and son arriving for The Sunseeker International Charitable Trust Ball - in aid of The Outward Bound Trust - at Battersea Evolution in south London. 2009
Robin Gibb and his wife Dwina at No.11 Downing Street in London for the Diana Awards.
British singer Robin Gibb arrives for the 46th Goldene Kamera (Golden Camera) media award gala in Berlin, Germany, Saturday, Feb. 5, 2011
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