A preliminary result of an autopsy conducted on Lisa Van Heuver, the Los Osos woman allegedly killed by her son, shows that trauma from the assault was the cause of death.

It appears strangulation will be “at least a contributing factor, but I do not know if it will be the only cause listed,” said Aaron Nix, Sheriff's Office spokesman.

The final report of the autopsy, which was conducted last week, is still being prepared, Nix said.

Michael Bret Van Heuver, 23, has pleaded not guilty to premeditated murder of his mother in San Luis Obispo Superior Court. She died May 15 from her injuries related to an assault on April 27.

The Sheriff’s Office is continuing its investigation into the attack. Lisa Van Heuver’s sister, Pamela Van Heuver, said her nephew had substance-abuse issues. Lisa was trying to help him get his life on track, she said.

Nix previously said deputies previously had been called to the home where Michael Van Heuver lived with his mother to respond to his "mental health issues."

Michael Van Heuver is scheduled to appear before Judge John Trice for a pre-preliminary hearing on June 7.