LONDON — In a case that is part parable of high-society travail and in part as a police-beat mystery, investigators awaited the outcome on Wednesday of further tests to discover what killed American-born Eva Rausing, one of Britain’s richest women, after her body was discovered at her upmarket home and her husband arrested.


The tale — entwining ultrarich philanthropists, a history of drug abuse and many unanswered questions — has seized British headlines since Monday. That was when Hans Kristian Rausing, 49, an heir to Tetra Pak, a multibillion dollar global food-packaging empire born of a milk carton, was arrested on suspicion of possessing illegal drugs. Mr. Rausing had apparently been driving erratically in south London.


But when the police went on to search the couple’s luxurious, five-story mansion in Cadogan Square, in the tony Chelsea district of London, they discovered the body of Ms. Rausing, 48. It was not clear how long she had been dead.


The Daily Mail tabloid and other British newspapers said on Wednesday that the body may have been undiscovered in a bedroom for several days. Newspapers published what they said were recent photographs of the couple looking “drawn and disheveled.” An initial post-mortem examination on Tuesday failed to establish a formal cause for the death.


Police officers were photographed on Wednesday lugging boxes of forensic equipment through the porticoed entrance to the Rausings’ stuccoed home, while another officer stood guard.


“Officers from the Homicide and Serious Crime command are investigating, and the death continues to be treated at this time as unexplained,” a police statement said.


Mr. and Ms. Rausing met while they were in rehab 25 years ago, and came to support many causes, including some associated with addiction. The BBC reported that Ms. Rausing, the daughter of a wealthy American soft drinks executive, was connected to the international drug abuse prevention charity Mentor, and that the couple financially supported the group Action on Addiction.


Four years ago, they gained notoriety when Ms. Rausing was caught with crack cocaine and heroin in her purse as she entered the American Embassy in Grosvenor Square here to attend a reception.


At that time, according to court records quoted by The Press Association news agency, a police search of their home unearthed further stashes of crack cocaine, heroin and cocaine.


The prosecution was later dropped and the Rausings were released with conditional cautions from the police.


At the time, according to British news reports, Ms. Rausing acknowledged “a serious mistake which I very much regret” and spoke of “the help that I very much need. I have made a grave error, and I consider myself to have taken a wrong turn in the course of my life.”


But in a public debate comparing punishments for rich and poor, Sir Ian Blair, at that time the head of Scotland Yard, as London’s Metropolitan Police force is known, said the use of cautions “sends entirely the wrong message about drug use and disregards the harm it does to communities.”


While the police have declined to formally identify the man they have arrested following the discovery of Ms. Rausing’s death, her husband has been widely identified in press reports and the police have given details of the case in response to questions about him.


He was initially held in a south London police station but has since been moved to a medical facility.


A statement from the dead woman’s family said her parents, Tom and Nancy Kemeny, “along with all of their family are deeply saddened by the death of their beloved daughter, Eva Louise Rausing.”


“Eva was a devoted wife for 20 years and mother of four much-loved and wonderful children.”


“During her short lifetime she had a huge philanthropic impact, supporting a large number of charitable causes, not only financially, but using her own personal experiences.”


“She bravely fought her health issues for many years,” the statement said, describing the family as “devastated.”


Her in-laws, Hans and Marit Rausing, said they were shocked and saddened. The elder Mr. Rausing built up the Tetra Pak empire from a company his own father founded in 1944, manufacturing laminated cardboard cartons that enabled milk to be kept fresh without refrigeration, and then creating other lightweight, inexpensive packaging used across scores of nations, like drink boxes.


A Forbes Magazine profile in March 2012 listed Hans Rausing Sr. as No. 88 on a list of the world’s billionaires, with a fortune of some $10 billion. The profile said Mr. Rausing sold his share of the business to his brother, Gad, for an estimated $7 billion in 1995, and to avoid punitive Swedish taxes, eventually moved to a 900-acre estate in rural East Sussex in southern England.