he city medical examiner's office said yesterday that it has been unable to determine whether a woman who vanished on the Upper East Side earlier this year and was found in the East River died in an accident, a homicide or a suicide, leaving unresolved one of the year's most perplexing mysteries.

The woman, Svetlana Aronov, 44, disappeared on March 3 while walking her father's black-and-white cocker spaniel, sparking an intensive investigation that at various times focused on the Russian mob, an enigmatic cabdriver and Ms. Aronov's husband, a 45-year-old hematologist who, like Ms. Aronov, had grown up in St. Petersburg, Russia.

The decomposed body of the 5-foot-4-inch, blond woman was found on May 6, floating under a pier on the East River behind a Long Island City restaurant; it was identified through dental records. The next day, an autopsy performed by the office of the city's chief medical examiner, Dr. Charles S. Hirsch, found that she had drowned, but it did not reveal the manner of her death, according to Ellen Borakove, a spokeswoman for Dr. Hirsch.

Yesterday, Ms. Borakove said that while the circumstances were suspicious, investigators have been unable to determine whether Ms. Aronov died as a result of an accident, a suicide or a homicide. "We don't have enough information or evidence to classify the manner of death," she said.

Detectives working on the case had hoped that after the two-month search for the missing woman, the discovery of her body would provide clues as to how she had died. But while investigators have pored over the dead woman's clothes and her effects — including studying her Cartier watch in an effort to determine whether it could tell them when she entered the water and examining bruises on her shins to determine where she might have gone in — they have been able to learn little about how she ended up in the river.

The determination, announced yesterday, puts the case back in the hands of the detectives from the 19th Precinct, who have been investigating the case since Ms. Aronov's disappearance.

And while the police long feared that Ms. Aronov, who was to pick her father up at the airport on the afternoon she disappeared, had been murdered, detectives more recently have begun to focus on the possibility that she might have been depressed and taken her own life, despite early indications that she had shown no signs of having mental problems.

Edward Hayes, a lawyer for Dr. Aronov, said the autopsy had determined that Ms. Aronov had no drugs in her system, but shed little further light on the woman's death. "We still have not solved what happened to her, and it's still a terrible mystery," he said.

Dr. Aronov came under scrutiny because homicide detectives always look first to the husband or wife when someone disappears, but investigators did not initially focus on him as a suspect.

As the weeks dragged into months, however, detectives became more interested in the doctor, who was at one of his offices in Manhattan and Brooklyn when his wife disappeared. He has denied wrongdoing.