"His downfall is almost operatic in its tragedy," says Grant Colfax, a Harvard-trained doctor who was once one of Arndt's closest friends. As Arndt prepares to stand two separate criminal trials, Col-fax is like many of the people who knew him well and are now left scratching their heads. Their emotions oscillate between two poles: There's the lingering disbelief that such a brilliant and compassionate doctor-some say the most brilliant and most compassionate they had ever known-could seem to self-destruct in such a spectacularly public way. Then, perhaps more troubling, there's that voice inside them, which had been muffled deep for so long, the one that kept telling them it was only a matter of time before David Arndt's self-absorption and sense of invincibility finally got the best of him.

David Carl Arndt was born on October 10, 1960, in New Haven. Kenneth Arndt was attending Yale medical school and living in student housing with his wife,Anne. Many of the other med students weren't even married yet, never mind parents. The couple's baby became an immediate attraction for Ken's classmates. "From the time he was extremely small, David was a very bright guy," says Jack Barchas, one of Ken's good friends at Yale and now chairman of psychiatry at Weill Cornell Medical College in New York. "And he just radiated happiness. We'd go over there for brunch-lox and bagels-and here was this little kid, always interacting."

When David was almost two, the Arndts packed up for Boston, so Ken could do his residency in dermatology at Massachusetts General Hospital. They had another child, a daughter. Ken would begin climbing the ranks of Boston medicine, joining the faculty of Harvard Medical School and eventually becoming chief of dermatology at Beth Israel Hospital. Years later, Anne, a psychologist, would also join the Harvard Med faculty. Friends describe the couple as charming, warm, stylish, and smart.

Growing up in Newton, David stood out. Extremely bright, no doubt about that. Tall too. Kathy Sias was his neighbor and one of his best friends. She ate dinner with his family, accompanied them on ski trips to their place in New Hampshire. Longhaired David was intense and intellectual but fun to be around. What did they do together? "A lot of drugs," she says, chuckling. "Just about everybody in our clique did during those days."

She and other friends say David, who attended Weeks Junior High School in Newton and the private Cambridge School of Weston, was always pushing limits. (He kept a boa constrictor as a pet, says Sias.) They also say Anne and Ken seemed hipper and easier for teens to talk to than other parents in the neighborhood. But Sias says that as she spent more time with the family, she changed her mind. "They were as unclued-in to teenagers as most parents, but they thought they were more clued in," she says. "His father was remote. His mother thought she knew everything because she was a psychologist. 'Oh, it's just a phase,' she would say about anything going on with David."

(Through their attorney, Stephen R. Delinsky, Ken and Anne Arndt declined to comment for this story, and David declined to talk beyond his brief conversations outside of the courtroom. "Dr. Arndt's parents respect, love, and admire him very much and are deeply concerned that your proposed article about David will seriously compromise his ability to achieve justice," Delinsky wrote. The couple "are confident that when all the facts are presented in court, David will be found not guilty in both cases.")

Though David would eventually become comfortable in his homosexuality, it's not surprising that his teenage years were more difficult.

"Looking back, I think he was aware of it, but I don't think he wanted to be," Sias says. "If he had admitted that he was gay, he would have probably lost a big part of his circle of friends." He dated girls, including Sias. "For about a week and a half," she says. "We went back to being best friends."

After logging time at the University of Massachusetts at Amherst from 1978 to 1979, Arndt left the state for San Francisco. He immediately soaked up the ethos of the city-part tie-dyed Haight-Ashbury hippie, part Tales of the City free spirit. The son of Harvard faculty members enrolled in a "university without walls" college called Antioch West. The downtown school awarded students course credit for their life experience. It no longer exists. He quickly earned a bachelor's degree and became a mental health counselor, working with the homeless who, in the parlance of San Francisco, were housed in "homeless hotels." Arndt's living quarters weren't much better.

On April 7, 1982, Arndt married a woman from India named Shobha Hundraj Nagrani. They would file for divorce four years later, and it became official in December 1987. Many of his friends say they knew little about the circumstances surrounding the marriage. What they did know about Arndt during this period was that he was into writing, literature, the arts scene. He was passionate, smart, insightful, alive.

And arrogant.

"One of a kind," says Harvey Peskin, who was a professor in San Francisco State University's clinical psychology graduate program when Arndt enrolled in 1983. What set him apart was the way he put everyone around him, especially the professor, on notice. "Professors tend to believe that students have to work to earn their respect," Peskin says. "David felt that the professor was the one who had to earn the right to have his respect."

As the yearlong class wore on, Peskin, who had initially been irritated by Arndt's chutzpah, found himself wanting to pass his brilliant student's test. David Arndt has that effect on people. "I don't think his behavior changed much," Peskin says, "but I think I changed."

But Arndt would begin changing in other ways. One day in 1983, he walked into a San Francisco clinic where Stephen M. Goldfinger, a psychiatrist who oversaw mental health services for the homeless, was presiding over a case conference. Afterward, they talked, and soon they were dating and then living together. Goldfinger was thirty-two, Arndt twenty-three.

Arndt earned his master's degree and turned in his tie-dye for extensive travel throughout Asia, gourmet cooking, and an intensified focus on his career. He began contemplating medical school and took some supplemental pre-med classes.

It was around this time that Jack Barchas got a call from Ken Arndt. Barchas was then the director of a prestigious research laboratory at Stanford. His old Yale med school pal told him that David was living in California and for the first time was thinking about pursuing medicine. "Ken, it's probably easier for me to talk to him about it than you," Barchas said. "Have him come see me."

As it turned out, Barchas's lab had just been given a very early and crude MRI machine, which the researchers were about to experiment with using rats. Arndt volunteered to help. In no time, he had all but taken over the project. "He was like a navy SEAL," Barchas recalls. "Just willing to do it and not waiting to be told." Arndt suggested to Barchas that they write an academic paper about their findings. When it was published, the name of David Arndt was listed first, followed by a bunch of respected researchers with actual titles after their names.

Years later, when Barchas was serving with Ken Arndt on the editorial board of the Journal of the American Medical Association,and he would ask about David, Ken would say, "It's all coming together for him."

In 1988, David Arndt came home. He made his way to the hallowed ground of Harvard Medical School, where his father, one of the nation's top dermatologists, was a heavyweight. If relations between him and his parents had been strained during some of his time in San Francisco, they appeared to be back on track. But David didn't advertise his connections. Occasionally, a classmate would notice the author's name on their dermatology textbook. "Kenneth A. Arndt-any relation to you?"