(CNN) Authorities say the founder of an African American museum in Baton Rouge, Louisiana, who was found dead in the trunk of her car last week, had been suffocated.

The body of Sadie Roberts-Joseph was recovered about 3:45 p.m. Friday after an anonymous caller reported finding her, Baton Rouge police spokesman Sgt. Don Coppola said. The preliminary cause of death was "traumatic asphyxia, including suffocation," the East Baton Rouge Parish Coroner's Office determined following a Monday autopsy.

The 75-year-old did not die by strangulation, coroner Beau Clark told CNN, saying without elaboration that her nose and mouth were blocked. Asked if he found any wounds on her body, Clark said he is not releasing any such details at this time. A toxicology report will be available in three weeks, he said.

Roberts-Joseph's family had seen her earlier that day, Coppola said.

She was found in the truck of her car, which was about 3 miles from her home, according to Baton Rouge police.

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