Why Mary Richardson Kennedy’s Family Opened an Investigation Into ‘Unanswered Questions’ About Her Death After Her Suicide (Exclusive)

Isabel Vincent’s biography ‘RFK, Jr.: The Fall and Rise’ details the months leading up to Mary’s death at age 52

NEED TO KNOW

• Isabel Vincent’s biography RFK, Jr.: The Fall and Rise reveals details about RFK Jr.’s tumultuous marriage to Mary Richardson Kennedy and her 2012 death by suicide

• Mary’s family hired investigators after her death to explore “unanswered questions”
• “There was a real divide, and I think that they just felt he was insensitive to what was going on with her,” Vincent tells PEOPLE in an exclusive interview

An upcoming biography of Robert F. Kennedy Jr. reveals new details of his private life, including the days leading up to the 2012 suicide of his second wife, Mary Richardson Kennedy.

Investigative journalist Isabel Vincent's book, RFK, Jr.: The Fall and Rise, is out on April 14, and is partially based upon the health secretary's death at age 52.

The book, in part, recounts the couple's tumultuous marriage. Three days after RFK Jr. filed for divorce in 2010, Mary was arrested for driving while intoxicated.

“Mary did not want a divorce, and she did not want to lose custody of her children,” Vincent writes. “Following her arrests, she attended AA meetings, but most of all, she pored over Kennedy's diaries. In many ways, she was trying to reassure herself that she had been married to a chronic philanderer for nearly 20 years.”

On May 16, 2012, Mary was found dead by hanging in the barn of the couple's Bedford, N.Y. home, by RFK Jr. and Mary's friend, Shannon White. When some of Mary's siblings arrived at the house hours later, Mary's sister, Nan Richardson, told RFK Jr., “You have killed my sister.”

“There was a real divide, and I think that they just felt he was insensitive to what was going on with her,” Vincent tells PEOPLE in an exclusive interview, adding that the Richardson family was “horrified by everything that happened.”

Mary was initially buried in Saint Francis Xavier Cemetery in Centerville, Mass., beside Sargent Shriver and Eunice Kennedy Shriver. Days later, RFK Jr. had her remains moved to an unmarked plot at the edge of the cemetery.

Per the book, the Richardson family hired a private investigation firm and a former homicide detective after the funeral, to look into “unanswered questions” related to Mary's death.

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“The firm wanted to know where she had obtained the rope used in her hanging and whether she knew how to tie a nautical knot,” writes Vincent. “They also asked about Kennedy's movements and his relationship with his estranged wife, according to sources who were interviewed by the firm."

The investigation did not turn up any new details, ending the possibility of a wrongful death lawsuit. Friends of RFK Jr., however, said that Mary's death “weighed heavily” on him, despite his new relationship with actress Cheryl Hines, who he began dating while he was separated from Mary.

“I know Bobby well enough to know that Mary's suicide is a weight he will carry for the rest of his life,” a former friend said, per the biography. “That's going to haunt him.”

RFK, Jr.: The Fall and Rise, based upon over a decade of research, details its subjects' private battles, including his past drug addiction, grief over the 1968 assassination of his father, Robert F. Kennedy and navigating his family's complex legacy.

RFK, Jr.: The Fall and Rise arrives on April 14 and is now available for preorder, wherever books are sold.

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