Police are investigating the cause of a car accident that killed two women and injured a third this week when their vehicle crashed into a tree on the Kennedy family’s private estate in Aquinnah.

The driver of the vehicle, 70-year-old Judith Morse of West Tisbury, and front-seat passenger Susan S. Lambard, 69, of Lyman, N.H., were rushed to Martha’s Vineyard Hospital just after noon on Tuesday, where they were pronounced dead. The rear-seat passenger, 68-year-old Susan Papanicolaou of Minneapolis, sustained minor injuries.

A preliminary investigation of the crash indicates Ms. Morse was reversing her 2000 Land Cruiser down a private driveway at 2 Red Gate Farm when she lightly backed into a tree, state police said this week. “She then attempted to drive forward when the vehicle struck an electrical box and a porch attached to a garage, and then traveled down a hill and struck a tree head on. The total distance was approximately 319 feet.”

“She apparently put the car in drive and we believe she just accelerated from there,” state police Sgt. Thomas Medeiros told the Gazette. “It was just a perfect storm.”

“It’s one of those freak accidents,” said Aquinnah police chief Randhi Belain. “It’s bizarre.”

Police who responded to the scene Tuesday said Ms. Morse, her sister, Ms. Papanicolaou, and their childhood friend, Ms. Lambard, were attempting to explore Red Farm Gate, the secluded 366acre Kennedy compound, when they came upon several buildings and the property’s caretaker, Albert Fischer.

Mr. Fischer later told police he did not speak with the women, turned his head, and lost sight of the car. He then drove out to the main road, Moshup Trail, in an unsuccessful attempt to locate the women. When he returned to the Kennedy property, he noticed that an electrical box had been overturned. He found the women’s wrecked car at the bottom of a hill near Red Gate Farm Road at 12:10 p.m.

Within moments of calling the police, Mr. Fischer was joined by Chief Belain, Aquinnah Police Sgt. Paul Manning and state police Sgt. Medeiros at the location of the accident. Mr. Belain said the men were expecting to find a minor collision in the often quiet area. Instead, they found Ms. Morse and Ms. Lambard in need of serious medical attention, and Ms. Papanicolaou administering first aid.

Dispatchers alerted the hospital to prepare for two priority-one patients, a code that indicates a patient is critically ill or injured. The Aquinnah police and fire departments, Sgt. Medeiros, tribal rangers, Tri-Town Ambulance, Chilmark firefighters and paramedics from each of the towns also responded.

Sgt. Medeiros said a state police accident reconstruction team and crime services traveled from off-Island later in the day, gathering information in attempt to piece together the sequence of events. State police are now looking into several possible contributing factors as to why Ms. Morse accelerated after backing into the tree, including driver error, a medical incident or a mechanical issue.

“The findings of the collision reconstruction team and medical evidence will help determine the cause,” the state police said.

The news of the dramatic crash, which came just days after a double shooting in West Tisbury, rattled the quiet Island for the second time in less than a week. On Wednesday, the Martha’s Vineyard Museum released a statement to board members expressing sympathy for the family of Ms. Morse. Her son, Chris Morse, is a longtime museum board member and owner of the Granary and Field Galleries in West Tisbury and the North Water Gallery in Edgartown.

The John F. Kennedy Library Foundation also released a statement from Caroline Kennedy and Edwin Schlossberg, who now own the estate first purchased by Jacqueline Kennedy Onassis in 1978. “Our thoughts and prayers are with the families of the victims of this tragic accident,” they said.

Tomorrow, all those who responded to the scene of the accident have been invited to a debriefing at the Aquinnah Fire Department, where a team of experts from Cape Cod will provide tips and offer support on dealing with stressful situations.

“It was a tragic accident,” Sgt. Medeiros said.