On Dec. 27, 1979 the very wealthy Sunny von Bülow, 50, lapsed into a coma on her Newport, R.I. estate, following an apparent insulin injection. She recovered on that occasion, but a year later, after a similar incident, she could not be roused, and now she lies in an endless sleep in a New York hospital. Last March, after failing to convince a jury that his wife's abuse of drugs and liquor had caused both comas, Claus von Bülow, 55, was convicted of attempting her murder. The Cambridge-educated lawyer and boulevardier, who is free on $1 million bail, faces 30 years in jail. Meanwhile his attorneys are preparing an appeal and seeking new evidence. Writer Truman Capote, who delved into the psychology of crime in the 1966 best-seller In Cold Blood, befriended Sunny in the '50s. Now he has come forward with stunning information to buttress the defense.

"I told my friends during the trial that I felt a terrific sense of guilt, that I really should get in touch with Claus' lawyers," Capote admits. "But I presumed the defense would come up with a strong case—lots of people knew the truth about Sunny. I was also put off by Norman Mailer's involvement with murderer Jack Henry Abbott. I didn't want to be like Norman Mailer, who behaved foolishly." The conviction changed Capote's mind. Last week, in an exclusive interview with PEOPLE's Gioia Diliberto, he drew a portrait of Sunny strikingly different from the temperate woman depicted by her faithful servants at the Newport trial.

I was spending a weekend in the early '50s with C.Z. and Winston Guest on Long Island, and Sunny came to lunch. She was a very pretty, radiant girl, somewhat shy. After lunch she and I went on a long walk. This was the beginning of our friendship.

A week later I had lunch with her in New York. I mentioned I had to go to the doctor every day to have vitamin shots. She said, "Why don't you give the injections to yourself?" And I said I wouldn't have the faintest idea how to do that. "There's nothing to it," she replied. "I'll teach you. I do it all the time." This was when we began to have a mutual confidence about the drugs we were taking.

At the time I was going to Dr. Max Jacobson, the original Dr. Feelgood [whose medical license was revoked in 1975 for improper prescription of amphetamines]. Ostensibly, he was giving me vitamin injections, but actually, they also had amphetamines in them. One day Sunny was trying to show me how to inject myself by giving herself one of my injections. Right away she said, "This is half amphetamine." "How do you know?" I asked. "Because I've been giving myself amphetamine injections intermittently for a long time," she said. So you can't say the girl didn't know anything about drugs.

Similarly, Sunny was really deep into drinking. She told me so, and since my mother was an alcoholic, I'm intensely sensitive to all the subtle little things that are different between just drinking and being alcoholic. With Sunny there was a compulsion. When she started drinking she just went on, whether she wanted the drink or not.

After several years of monthly lunches Capote lost touch with Sunny in 1957. That year she had married Prince Alfred von Auersperg and moved to Austria. Two decades later, after her divorce, her return to the U.S. and marriage to Claus von Bülow, the two old friends ran into each other one afternoon in the late '70s on New York's Madison Avenue.

It was a very affectionate reunion. We walked up the block together and Sunny suggested we go to Bemelman's Bar at the Hotel Carlyle. When we sat down, she said, "Do you remember that drink we used to love, the dry Manhattan? It was dry vermouth and Southern Comfort." She had seven or eight of them as we sat there, and I had three.

Sunny said she was depressed most of the time. I don't think it had anything to do with von Bülow. Although Sunny could be very merry, and laugh if you told her something that amused her, there was always an underlying tristesse, a kind of sadness that no one would ever solve. Actually, her conversation about von Bülow was pleasant. "He's very amusing and a good writer," she told me.

That day we talked about drugs. Sunny said she had never liked cocaine and that she had only taken it a few times. However, there was something she did like. She called it a "roller coaster." As she explained it to me, it was Demerol mixed with amphetamines. She didn't tell me where she got the drugs. She said she'd been doing it for several years, and that she liked it better than anything she'd ever done. She also talked about grinding down Quaaludes and mixing them with distilled water and amphetamines.

Then she told me about a book called Recreational Drugs. I tried to find it in several bookstores and couldn't. A week after this meeting I spoke to Sunny on the phone. That was the last time I talked to her. She sent me a copy of the paperback. It lists every drug you can think of and describes what each does and what's the maximum dosage you can take safely. It was a compendium and definitely accurate about every drug I've taken.

Now, this woman was not stupid in any way and she was definitely not stupid about drugs. Whether it was an accident or she did it on purpose, my own theory is that she gave it to herself.