A woman found dead in the trunk of a car Friday evening was the founder of Baton Rouge's African American history museum who helped jumpstart annual Juneteenth celebrations during her work as "a tireless advocate of peace."

Baton Rouge police said Saturday morning that the body of Sadie Roberts-Joseph, 75, had been found in the 2300 block of North 20th Street, about three miles away from her home. The cause of death has not been determined.

Click here for more: Autopsy: Sadie Roberts-Joseph, founder Baton Rouge African American history museum, suffocated

The Baton Rouge Police Department mourned Roberts-Joseph in a Facebook post not long after releasing her name, calling her "a treasure to our community."

"Our detectives are working diligently to bring the person or persons responsible for this heinous act to justice," the agency said.

State Rep. C. Denise Marcelle said in a Facebook post that that Roberts-Joseph had raised awareness of African American history and the civil rights movement. "My heart is empty … as I learned last night that Ms. Sadie Roberts Joseph was found murdered!" Marcelle wrote. "This woman was amazing and loved her history. She never bothered anyone."

Roberts-Joseph founded the Odell S. Williams Now and Then African-American History Museum in 2001. The museum, now known as the Baton Rouge African-American History Museum, is part of the New St. Luke Baptist Church campus on South Boulevard, where Roberts-Joseph's brother serves as pastor. It sits in the shade of elevated Interstate 10 that bisects the historically black neighborhood of Old South Baton Rouge.

Roberts-Joseph also organized an annual Juneteenth festival at the museum. She told The Advocate during the 2018 celebration that she led a "rebirth of Juneteenth" in 1991. The day commemorates June 19, 1865, the day Union soldiers delivered belated news of President Abraham Lincoln's Emancipation Proclamation to Texas. The document had been signed more than two years earlier, on Jan. 1, 1863 — declaring that all slaves in the South were free.

"News of freedom trickled down very slowly," Roberts-Joseph said in 2018.

Through her decades of leadership in the Baton Rouge area, Roberts-Joseph presented a consistent message of unity and togetherness aimed at, in her words, helping communities "heal from the legacy of slavery and move forward." She encouraged black residents to embrace their heritage, acknowledge past injustices and use their voices to close racial divides and create a brighter future: "If you don't know where you come from, you don't know where you're going."

"We have to be educated about our history and other people's history," she told The Advocate in 2016. "Across racial lines, the community can help to build a better Baton Rouge, a better state and a better nation."

She celebrated the election of President Barack Obama, who is featured prominently in the museum. She said his presidency "gives children in particular a sense of hope. As we inspire and as we educate them, we will see our youth doing greater things."

Just a month before her death, Roberts-Joseph was photographed doing what she loved: educating Baton Rouge residents about their heritage at this year's Juneteenth celebration. She led a procession to the Mississippi River to raise the official Juneteenth flag as part of an effort with 45 other states and Washington, D.C., to create a national holiday.

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On Saturday morning, Beatrice Johnson, one of Roberts-Joseph's 11 siblings, tried to absorb the tragic and unexpected loss. Johnson lives just two doors down from Roberts-Joseph's home on a quiet street in Scotlandville and said she saw her sister often.

"She would come by here every day," Johnson said. "Friday, she came by (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," Johnson said, gesturing toward her kitchen. "She never came back to get it."

The siblings grew up in Woodville, Mississippi, before their family moved to Baton Rouge. Roberts-Joseph attended the Baton Rouge Vocational-Technical School and Southern University, where she studied education and speech pathology. She later served in several volunteer roles within the local black community and as minority business officer for the city of Baton Rouge. She worked for decades as a certified respiratory therapy technician.

Roberts-Joseph is survived by two children, Jason Roberts and Angela Roberts Machen, who is a commissioner on the Greater Baton Rouge Port Commission.

Johnson said she had already lost two brothers within the past year. On Friday she learned about the loss of her big sister.

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In addition to the Juneteenth festival, Roberts-Joseph organized an annual Veterans Day celebration at the Port Hudson National Cemetery, honoring veterans of all races who fought in the Civil War.

"When I try to do something, God always opens doors, and I try to do the very best that I can, not necessarily for me but particularly to help inspire and educate the younger generation," she told The Advocate at the ceremony in 2016. "I find gratification that we are coming together and realizing our differences are not as great as our commonalities."

A community activist, Roberts-Joseph also ran, in two unsuccessful bids, for Louisiana public office, for the U.S. Senate in 1996 and for lieutenant governor in 1999.

Together Baton Rouge said in a statement Saturday that "while her death is a tragedy, it would be an even greater injustice to let her death overshadow her tremendous life that left behind a legacy of activism and black pride that endeared her to the Baton Rouge community."

"She was what was right about Baton Rouge and the magnitude of her loss to our whole community is a testament to that," the Together Baton Rouge coalition of church congregations and community organizations said.

Baton Rouge police described her as "a tireless advocate of peace."

Roberts-Joseph died as Hurricane Barry approached the state and residents made final preparations for possible flooding. But Johnson said she had more on her mind.

"Yesterday was a storm enough for us," she said.

Police are asking anyone with information on the case to call the Police Department at (225) 389-4869 or Baton Rouge Crime Stoppers at (225) 344-7867.