(CNN) -- The son of one of the world's wealthiest men is under arrest in London after the body of his American-born wife was found in their home this week, her death unexplained.
Police stumbled into the mystery Monday, when they arrested Hans Kristian Rausing on drug charges.
A search of his home in one of London's most expensive neighborhoods turned up the body of his wife, Eva, spurring police to arrest him again in connection with the death.
Eva Rausing had struggled with drug addiction for years, an acquaintance said.
"This has been an existing problem for a long time," said Liz Brewer, who knew Rausing through charity and social circles. "I think the whole thing is a complete tragedy."
The case puts the multimillionaire couple squarely back in the headlines four years after they were arrested on charges of possessing cocaine and heroin, according to media reports at the time.
Eva Rausing had tried to smuggle a small amount of crack cocaine and heroin into the U.S. Embassy in London, reports said. She and her husband were arrested when police found more drugs at their house.
The pair, however, avoided prosecution. Since then, they have kept a low profile, Forbes magazine said in its annual rich list report this year.
"It's very clear to us Eva had her own problems with drugs and drugs misuse," the head of an anti-drug organization told CNN Wednesday.
"She knew prevention was important. She knew how hard it was to get off drugs once you are on drugs," said Paul Tuohy, chief executive of Mentor.
Eva Rausing had donated hundreds of thousands of dollars to the charity in the years before her death, Mentor said.
Her husband is the son of Hans Rausing, who is worth an estimated $10 billion, thanks to the family's connection to Swedish packaging giant Tetra Laval.
Hans Kristian Rausing is now receiving medical treatment, police said Wednesday.
An autopsy Tuesday failed to determine the cause of Eva Rausing's death, police said.
Police refused to name Rausing as the man who was arrested, but a source familiar with the investigation said the man in custody lived at the address where the body was found.
The source asked not to be named discussing an ongoing investigation.
Eva Rausing gave more than 500,000 pounds ($778,000) to Mentor, said the charity, which runs programs "to protect children from alcohol and drugs."
Posts on a MySpace page dating back to 2007 that appears to belong to Rausing, but whose authenticity could not be verified, give a picture of her ups and downs.
She writes that she went to college in California. "I had a good time there -- too good, as I dropped out and did not go back to university until the grand old age of 24. Which leaves some troubled years in between ... The beginning was fun, the ending not so fun," she writes.
"I was lucky to have a loving supportive family who stood by me, though I didn't always see it that way at the time. So, I cleaned up my act, became a good girl, if maybe a little boring, got a degree in economics, and then got married!"
She says she is a good mother to the couple's four children but, in an apparent reference to her drug abuse issues, she writes of relapsing several years earlier.
"I fell back into the same hole as before and have been there for nearly 7 years. I once read that I would have 7 bad years (I don't normally believe in hocus pocus horoscopes) but so far it has been right, and I'm hoping for 7 good years starting 2007.
"I'm still married, amazingly, to a very kind, patient and loyal husband. I'm very lucky that he has stuck with me -- many would have not."
Hans Kristian Rausing's billionaire father was bought out of the Tetra Laval business founded by his own father.
Tetra Pak declined to comment on Eva Rausing's death or her husband's arrest because their branch of the family "divested its interests in Tetra Pak, and the Tetra Laval Group, in 1995."
CNN's Dominique van Heerden, Susannah Palk and Atika Shubert contributed to this report.