The body of Sadie Roberts-Joseph, 75, was found on Friday, but it was not immediately clear what led the officers to the car. The cause of death is still unknown, the police told the station.
Roberts-Joseph was a well-known lawyer in the Baton Rouge area. She founded the Odell S. Williams Now and Then African American Museum in 2001, where she has been hosting the city's Juneteenth Celebration for years.
She also founded Community Against Drugs and Violence, a nonprofit organization to create a safe environment for children in North Baton Rouge.
Local politicians, lawyers and community members mourned Saturday for Roberts-Joseph's death to expand their museum.
"Yesterday we lost a cultural legend! #RIP Sadie Roberts Joseph, "wrote the group. From the revival of Juneteenth to the preservation of culture in her museum, she was a trendsetter and icon in this city. "Call the police under 225-389-4869 or detectives under 225-344-STOP (7867).