Sadie Roberts-Joseph "was an amazing lady and just a great community figure," police Sgt. Don Coppola Jr. tells PEOPLE
Sadie Roberts
Sadie Roberts-Joseph
| Credit: Arthur D. Lauck/The Advocate via AP

Louisiana police are investigating the slaying of a well-known community and civil rights activist who founded an African American history museum in Baton Rouge.

Sadie Roberts-Joseph, 75, was found dead on Friday afternoon inside the trunk of her car, about three and a half miles from her Baton Rouge home.

Sgt. Don Coppola Jr. tells PEOPLE that the city’s police are investigating the death as a homicide.

“Right now we are investigating this to the fullest and waiting for new information to develop,” he says.

Preliminary autopsy results Monday determined that Roberts-Joseph died from “traumatic asphyxia, including suffocation,” according to the East Baton Rouge Parish Coroner’s Office.

Coppola says so far there is no known motive or suspects.

In a Facebook post, the police department wrote, “The Baton Rouge Police Department joins the community in mourning the loss of Ms. Sadie Roberts-Joseph. Ms. Sadie was a tireless advocate of peace in the community.”

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Roberts-Joseph’s sister Beatrice Johnson told the Associated Press that her sister had stopped by her home that morning because “she had mixed some cornbread, but her oven went out, and she brought it here to put in the oven.”

“The bread is still there,” she said. “She never came back to get it.”

Roberts-Joseph founded the Odell S. Williams Now and Then African-American History Museum — now known as the Baton Rouge African-American History Museum — in 2001.

She also was the founder of the non-profit Community Against Drugs and Violence and an annual Juneteenth Freedom Festival.

“She was such a big part of the community,” says Coppola. “The community is of course devastated by this and we are just searching for answers as far as who may be responsible for this. She was an amazing lady and just a great community figure.”

Anyone with information is asked to call detectives at 225-389-4869 or Crime Stoppers at 225-344-STOP (7867).