Kathleen McCormack Durst disappeared from her home in Westchester County nearly 34 years ago, on a cold January night, only months before she would have graduated from medical school. It was the beginning of an enduring mystery.

On Monday, Ms. Durst’s mother, Ann McCormack, who is 101, and three sisters — Carol Bamonte, Mary Hughes and Virginia McKeon — filed a $100 million lawsuit against the man they have long suspected of killing her: Robert A. Durst, her husband. The lawsuit contends that Mr. Durst violated the McCormack family’s right to sepulcher, a rarely used New York law granting family members the immediate right to possession of a body for burial.

“The family’s priority has been and continues to be to provide Kathleen with a proper and dignified burial,” Robert Abrams, a lawyer for the McCormack family, said.

The lawsuit contends that Mr. Durst “murdered Kathleen,” 29, his first wife. If successful, the lawsuit would strip Mr. Durst of much of his wealth; authorities put his net worth at about $100 million.