Jerome Barson, 78, was fatally injured when the vehicle in which he was a passenger crashed into the side of Williams' car in Palm Beach, Florida in June.
Barson's wife Linda, who was driving at the time of the collision, suffered a broken arm and other injuries while 38-year-old Williams was unhurt.
The Palm Beach Gardens police report said an unidentified third vehicle illegally cut off Williams as she tried to cross a busy six-lane highway near her home, setting off a chain of events that ended with the sedan being driven by Linda Barson slamming into the passenger side of Williams' SUV.
Police concluded that neither driver was at fault, but the Barson family dispute that Williams was driving legally and have filed a wrongful death lawsuit against the five-time Wimbledon champion.
Williams wrote on her Facebook page after the accident: "I am devastated and heartbroken by this accident.
"My heartfelt condolences go out to the family and friends of Jerome Barson and I continue to keep them in my thoughts and prayers."