A 75-year-old Louisiana woman who founded an African American history museum was discovered dead in the trunk of a car Friday afternoon, the Advocate reported.

“Our detectives are working diligently to bring the person or persons responsible for this heinous act to justice,” the Baton Rouge Police Department said Saturday in a Facebook statement.

Sadie 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, according to the Advocate. The museum is part of the New St. Luke Baptist Church campus on South Boulevard, where her brother serves as pastor, the outlet reported.

The website of the city’s visitor bureau says the museum features exhibits on African art, growing cotton, black inventors and a 1953 bus from the period of civil rights boycotts in Baton Rouge.

Baton Rouge police mourned the loss of Roberts-Joseph in its Facebook post, describing her as “a treasure” to the community.”

“Ms. Sadie was a tireless advocate of peace in the community,” the Baton Rouge Police Department said.

The police department said it had opportunities to work with Roberts-Joseph “on so many levels.”

“From assisting with her bicycle give away at the African American Museum to working with the organization she started called CADAV, (Community Against Drugs and Violence), Ms. Sadie is a treasure to our community,” whose “loss will be felt in the community,” the department said.