Questions over whether Claus von Bülow twice attempted to murder his multimillionaire American wife, or whether she was the cause of her own fate, are likely to re-emerge now that he has died, aged 92. Martha “Sunny” von Bülow, who died in 2008 after lying in a coma for 28 years, had collapsed in December 1980 at the couple’s Palladian mansion, Clarendon Court, on the Rhode Island coast at Newport. Claus was tried and convicted in 1982 on two charges of attempted murder, but the convictions were overturned on appeal in 1984. A second trial in 1985 acquitted him.

Tantalising questions nonetheless remain. Did he twice inject his wife with insulin, the central accusation? Or was she an alcoholic drug addict who, perhaps accidentally, inflicted her own destruction? Why did Claus hide the never explained “little black bag” containing syringes and an assortment of illicitly obtained drugs? Why, during Sunny’s first collapse, was he reluctant to summon a doctor? And did his mistress’s marriage ultimatum, combined with expectation of a large legacy from his wife’s death, propel him towards murder?

This was the first such court case to be televised in the US, and more than 70 hours of it was broadcast by CNN. American commentary during the five-year media spree that accompanied the case compared it to a soap opera, especially as Claus’s beautiful mistress, Alexandra Isles, had acted in a popular 1960s soap series called Dark Shadows. Soap-style, the case displayed an arrogant, unfaithful husband and an extravagantly self-indulgent wife, both people with immense riches but little to do.

A book by Claus’s lawyer, Alan Dershowitz, about the case, Reversal of Fortune (1985), was made into a 1990 film of the same name, starring Jeremy Irons – who won the best actor Oscar for his portrayal of Claus – and Glenn Close as Sunny.

Facebook Twitter Pinterest Martha “Sunny” von Bulow died in 2008 after lying in a coma for 28 years. Photograph: AP

Born in Copenhagen, Claus was the son of the Danish playwright Svend Borberg, a Nazi sympathiser whose family wealth dissipated between the wars, and Jonna Bülow, whose ancestors were German nobility. Between Swiss boarding schools, Claus found himself at 14 in Nazi-occupied Denmark, from where his mother smuggled him to the UK. He graduated in law from Trinity College, Cambridge, in 1946, and, after a short break, practised as a barrister for nine years – Lord Hailsham was his head of chambers – then became executive assistant to the oil billionaire J Paul Getty.

When Claus met Sunny, she had recently been divorced from Prince Alfred von Auersperg, with whom she had a son, Alexander, and a daughter, Annie Laurie, known as Ala. The couple married in 1966 and in 1970 settled in the 20-room Clarendon Court with the two Auersperg children and their own daughter, Cosima, aged three. The marriage deteriorated, however.

On Boxing Day 1979, Sunny drank several eggnogs with Alexander, by then aged 20, and became disoriented. The following day her maid, Maria Schralhammer, was unable to rouse the unconscious Sunny. Claus, she later testified, declined to call a doctor. Eventually, at the hospital, doctors noticed her high level of insulin. Sunny was not a diabetic. The doctors concluded that insulin had been introduced, but did not suspect a crime. Schralhammer did, especially when she discovered the black bag containing syringes and drugs. She alerted Ala, who noted that the contents included a barbiturate and Valium.

Family suspicions grew when Schralhammer said she had also seen a vial marked “insulin”. Then Alexander found a syringe, its tip encrusted with insulin, a test showed.

On 21 December the following year, Sunny again collapsed at Clarendon Court, and next morning was found unconscious in her bathroom. She never recovered. The Auersperg siblings hired a former New York prosecutor, Richard Kuh, to investigate, and his evidence was vital in the 1982 trial. Sunny’s children, Schralhammer and Isles all testified against Claus. He was given a sentence of 30 years.

Facebook Twitter Pinterest Jeremy Irons and Glenn Close in the film Reversal of Fortune, 1990. Irons won the best actor Oscar for his portrayal of Claus von Bülow. Photograph: Pressman/Shochiku Fuji/Sovereign/Kobal/Rex/Shutterstock

Out on bail, he appealed, hiring Dershowitz, a Harvard law professor, whose team soon uncovered serious inconsistencies in prosecution testimony. He also introduced new medical evidence, and contested the judge’s damaging inadmission of Kuh’s notes. Dershowitz succeeded because, he said, he had demonstrated that Sunny’s family, unable to accept her possible self-destruction, “hired a private prosecutor to conduct a vendetta against her husband”.

A new trial was ordered. It began in April 1985, with Claus represented by the best defence money could buy: unlimited funds were provided by Sir Paul Getty, his old boss’s son. Using Kuh’s notes, the defence showed that Schralhammer originally said nothing about insulin and lied to protect her mistress. Experts testified that a syringe tip could not become encrusted with insulin unless dipped in it – a needle is always wiped clean when pulled from the skin.

Although acquitted, Claus faced a $56m civil suit from his stepchildren. He eventually agreed to divorce Sunny and forfeit any family money, to leave the country and give up all rights to write books or publicise the case, in exchange for Cosima’s inheritance, estimated at $30m.

He returned to London in 1987, where he lived well in Knightsbridge, gaining a reputation as a raconteur, mixing with friends in the moneyed elite and writing theatre reviews for the Catholic Herald. Peter Soros, the financier, once said of him: “Generally, he’s an all-round amusing fellow who’s capable of being outrageous. Invite him to lunch and you’ll get a good meal out of it. Or rather, he’d get a good meal and I’d get a good story.”

Cosima survives him.

• Claus Cecil Borberg von Bülow, socialite, born 11 August 1926; died 25 May 2019