(CNN) -- The son of one of the world's wealthiest men is under arrest in London after his American-born wife was found dead 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.
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, according to media reports at the time. 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 on 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."
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."