Louisiana cops hunting the killer of an African American history museum founder — who was discovered last week in a car trunk — planned an autopsy Monday in the "heinous" murder, as friends and lawmakers eulogized the civil rights activist as "a mother of the community."

Sadie Roberts-Joseph was discovered in a vehicle parked just three miles from where she lived in Baton Rouge, where she founded and served as curator of the Baton Rouge African American Museum, which opened in 2001.

Investigators have been tight-lipped about potential suspects or a possible motive, but two city politicians close to Roberts-Joseph — Baton Rouge Mayor-President Sharon Weston Broome and Louisiana Rep. C. Denise Marcelle — confirmed her murder in separate social media posts.

FOUNDER OF LOUISIANA AFRICAN-AMERICAN HISTORY MUSEUM FOUND DEAD IN CAR TRUNK: POLICE

Broome wrote on Instagram on Sunday she learned of the death "of a dear friend and a mother of the community" just as now-tropical depression Barry was bearing down on Louisiana.

Describing Roberts-Joseph's death as "such shocking news," Broome announced a $5,000 reward for information leading to the arrest of anyone connected to Roberts-Joseph's death.

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On Friday, Marcelle posted to Facebook that Roberts-Joseph "was found murdered."

"This woman was amazing and loved her history. She never bothered anyone, just wanted to expand her African American Museum downtown, where she continually hosted the Juneteenth Celebration yearly," she wrote.

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

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The Baton Rouge Police Department called the 75-year-old "a tireless advocate of peace in the community" and a "treasure" who will be missed.

Anyone with information is urged to contact the department at 225-389-4869.

Fox News' Paulina Dedaj contributed to this report.