ROBERT F Kennedy Jr told a detective that on the day before his wife hanged herself, she called him to say "everything was her fault".
"She told me that she was sorry for everything. She said that I was right about everything," Kennedy said in a police statement.
Mary Richardson Kennedy hanged herself on May 16, in a garage on their Bedford, New York, estate.
The statement from her husband, son of Senator Robert Kennedy and nephew of President John F Kennedy, was given the next day.
Much of the file was blacked out before being released, and it was not clear what Mary Kennedy was referring to by "everything".
When she died, the Kennedys were in the midst of a divorce and custody battle for their four children.
An autopsy report showed Mary Kennedy had antidepressants in her system.
Her death sparked a battle between Kennedy and his wife's siblings, who tried to take control of her remains and held their own memorial service. Kerry Lawrence, an attorney for the siblings, could not be reached for comment, his office said.
In his statement, Kennedy said that during the phone conversation on May 15, his wife "told me that she needed me to take care of her". He described her as "a great person" and said he'd known her since she was 14.
Kennedy also described a search for his wife after the housekeeper, sounding "very scared," called him to say she couldn't find her in the house.
After he searched the attic and the shore of a lake he heard a lot of screaming coming from the garage.
Someone told him not to go inside, but he did and saw his wife. Kennedy's details of the discovery were blacked out, but other papers in the file show that Mary Kennedy was found in black gym clothes. Three metal crates and a metal ladder were on the floor.