The report from the Westchester County, N.Y., medical examiner came after the Bedford Police Department said in a statement it is still investigating the incident to learn what led to the hanging.
Bedford police confirmed Wednesday they were called to "an outbuilding" at a local address owned by Robert F. Kennedy Jr. to investigate an unattended death.
The couple married in a civil ceremony in 1994 when Mary Richardson, a designer, was six months pregnant and a month after Kennedy divorced his previous wife, CNN said Thursday.
Robert Kennedy filed for divorce two years ago, but the couple was still married at the time of her death, Kerry A. Lawrence, her family attorney, said.
Celebrity Families of 2014 [PHOTOS]