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Days after Casey Johnson was found dead in her Los Angeles home on January 4, her younger sisters Jaime, 27, and Daisy, 22, flew out from New York City to begin the sad process of sorting through her belongings. "We found a [to–do] list on her bedside table," says Jaime through tears. "Casey wanted to work in Kazakhstan with an orphanage. She wanted to have a vet clinic. She wanted to do stuff with diabetes. She was so close."

Close, that is, to reclaiming a life that had gone frighteningly off the rails. Born to immense privilege, the 30-year-old Johnson & Johnson heiress—whose family is worth $13 billion—seemingly lost her bearings when she moved to L.A. in 2001, seeking fame as an actress. Despite coping with severe diabetes since childhood, she was partying hard with pals Paris and Nicky Hilton, had been admitted to rehab, was dating women and men and had recently announced her engagement to reality show star Tila Tequila. By the time of her death, from what police believe was diabetic shock (toxicology reports are pending), she had lost custody of her daughter Ava-Monroe, 3, to her mother and hadn't spoken to her father for two years. "We were concerned," says one close friend. "She was so messed up."

In the days after her death, questions multiplied. Was Casey, as her sister Jaime believes, a "generous spirit" on the verge of straightening herself out? Or a poor little rich girl with demons so fierce that her tragic end, as one friend puts it, "didn't surprise anyone who knew her"? And how did the golden girl become a Hollywood cautionary tale?

Growing up on Manhattan's Upper East Side, the oldest daughter of New York Jets owner Robert "Woody" Johnson and ex-model Nancy Sale Frey was "a delightful, dimple-faced child," says newscaster Chuck Scarborough, a family friend. The Johnsons lived in a Fifth Avenue triplex, repairing on weekends to a New Jersey farm. "Casey had great cards dealt to her," says Joan Rivers, another family friend. "Looks and money."

Diabetes, diagnosed when she was 8, darkened the picture. Casey learned to give herself insulin shots, recalls Jaime, now a New York-based photographer, "but it was hard when she became a teenager. She wanted to be like everyone else—and she wasn't." In high school, dubbed "The Duchess" by friends for her impeccable style, "Casey was obsessed with looks and superficial stuff," says a source.

That obsession intensified when she landed in L.A. after dropping out of Brown University. But Casey quickly learned how hard it was to catch a break. She turned down a spot on the show The Simple Life, which made pals Paris Hilton and Nicole Richie household names, and later regretted it. The Hollywood scene also distracted—and enticed—her and landed her in rehab for substance abuse more than once. "She liked to push boundaries," often chasing all-nighters with a 16-hour sleep, says a friend. And she never felt pretty enough. One source says Casey had both breast implants and liposuction.

In 2007 Casey adopted Ava-Monroe, a baby girl from Kazakhstan named after her idols Ava Gardner and Marilyn Monroe. "She loved Ava," says Casey's friend Brittny Gastineau. But being a parent didn't come naturally. "Casey loved buying Ava stuff," says another pal. "But she didn't know how to feed her."

As Casey went on shopping sprees instead of paying bills, the family cut her off from her allowance, and Casey's mom took custody of Ava last fall. "Her parents consulted counselors," says a family source. "They were told she needed to hit bottom before she could bounce back." In November Casey was arrested for breaking into an ex-girlfriend's home and stealing clothes. But by the end of 2009 there were signs of hope. With Ava under Sale's supervision, Casey and her mom reconnected and "would talk every day," says Jaime. Adds a friend: "The feeling was that she recently reached a turning point."

Where it might have led, her devastated family will never know. Lost in grief, they take comfort in Ava, who doesn't yet know about her mother's death. "My mom's trying to figure out the best way to explain it," Jaime says. "She's teaching Ava about angels right now." Jaime plans to teach her something else. In the memories of the family who never stopped loving her, Jaime says, "Casey will stay with us forever."

  • Contributors:
  • Reported by Mary Green/New York City,
  • Charlotte Triggs/New York City,
  • David Caplan/New York City,
  • Amy Elisa Keith/New York City,
  • Alyssa Shelasky/New York City,
  • Howard Breuer/Los Angeles.