In a statement issued Tuesday, DPS Commissioner Frank Perry said a trooper involved has been placed on administrative duty with pay pending the outcome of the probe.
Perry offered his condolences to the family of 62-year-old Carolyn Ann Watkins.
"This is a multi-jurisdictional investigation and has the full attention of the Department of Public Safety administration. We will release accurate information to the public as soon as available and appropriate. At this early stage, our main concern is to conduct a thorough and professional investigation so we can determine exactly what happened. In addition, DPS is expeditiously conducting its internal review with the [State Bureau of Investigation]," said Perry.
DPS said the SBI investigation is an independent probe done at the request of the Johnston County District Attorney.
Perry said Trooper M.D. Williams - a 9-year Highway Patrol veteran - filed the crash report after Watkins' 2000 Pontiac was discovered down an embankment along Swift Creek Road - about five miles outside Smithfield - last Friday.
Williams' report - obtained by ABC11 - says there was no driver at the scene of the crash.
Sources tell ABC11 Trooper Williams had the car towed, but apparently didn't spot Watkins in the vehicle before it was hauled away.
ABC11 spoke with Watkins' family Tuesday. They said her body was found after they reported her missing to police, and the vehicle was searched at the tow yard.
"Maybe she could still have been alive, but she sat in that impound lot from Friday to Monday. It's sickening and it hurts," said Watkins' son Wooten.
The family said Watkins - a grandmother of four - was perfectly healthy, and they don't know what could have caused her to drive off the road. They said they suspect she may have been hidden by the car's air bags - which deployed in the crash.
Still, they say officers should have searched the car, and they want answers.
An autopsy is pending to see how and when Watkins died.