Baton Rouge police said in a statement that Sadie Roberts-Joseph was a "tireless advocate"

Sadie Roberts-Joseph's sister remembers her as a woman who made things better - who led neighborhood trash cleanups and house repairs, who launched a local group to fight drugs and violence, who founded a black history museum because, as Roberts-Joseph liked to tell everyone, "If you don't know where you came from, it's hard to know where you're going."

That legacy was on Beatrice Armstrong-Johnson's mind Sunday as she thought about how her 75-year-old sister died. Police found the body of the community leader and activist - a prominent voice in the push to make Juneteenth a state and national holiday honoring the freeing of America's slaves - in a car trunk Friday, about 3 miles from her home in Baton Rouge.

"She was a total advocate of peace, love and harmony, and she died just the opposite," Armstrong-Johnson, 68, told The Washington Post on Sunday.

Police are investigating and do not know the cause of the death, the Baton Rouge Police Department said in a statement Saturday.

The East Baton Rouge Parish Coroner's Office will release a preliminary cause of death Monday, chief of investigations Shane Evans told The Post.

News of Roberts-Joseph's death has brought an outpouring of grief and disbelief from friends, family and local officials familiar with her passionate advocacy for the preservation of black history.

Sunday rain pelted Kaufman Street, where the sisters lived two doors down from each other.

A tree was knocked down on the side of the dead-end street, and sandbags lined doorways braced for flooding. Plants crowded Roberts-Joseph's front yard, and a plaque listing the Ten Commandments was set on a green porch wall.

One door over, Debbie Magee grieved for her neighbor of 13 years.

"She was the epitome of good. She stood for something," said Magee, 39, as her 4-year old son, Lorenzic, played at her feet. "She wanted to make sure we weren't judged on the ZIP code we're in."

Roberts-Joseph warded off suspicious people on the street and always had a piece of fruit or a toy for kids in the Scotlandville community, Magee said. And she stood by a local elementary school so often - handing out paper and pencils to children - that you could mistake her for a crossing guard, Magee said.

"She did not deserve for someone to take her life and then place her in a trunk and leave her there. That's not right," Magee said as tears filled her eyes. "She will truly be missed."

Roberts-Joseph's work brought her into contact with leaders such as President Barack Obama and civil rights activist Jesse Jackson, her sister said.

"My heart is empty," Louisiana Rep. Denise Marcelle, a Democrat, wrote on Facebook after learning what had happened. The Baton Rouge branch of the NAACP mourned the loss of a "Cultural Legend" - a "trendsetter and icon" in the city where Roberts-Joseph revived Juneteenth celebrations and established her museum, the group said.

Baton Rouge police said in a statement that Roberts-Joseph was a "tireless advocate" who worked with the department on things such as a bicycle giveaway at her museum and the neighborhood organization she founded, Community Against Drugs and Violence (CADAV).

Another major part of Roberts-Joseph's legacy: her dedication to the Odell S. Williams Now and Then African-American History Museum, which she founded in 2001 and ran with volunteer help and donations. The Baton Rouge museum spotlighted black history and hosted gatherings for holidays such as Memorial Day, Kwanzaa and Juneteenth.

"It is exciting to see Juneteenth grow in popularity and support as America's 2nd Independence Day celebration," Roberts-Joseph said in 2002, when she was director of the Louisiana Juneteenth Holiday Campaign.

The museum, which features a brightly colored bus and paintings on its blue fence, sits next to the Baptist church where Roberts-Joseph's brother serves as pastor. The museum is closed Sunday - but if someone at the services wanted to pop in, Roberts-Joseph opened the space up, Armstrong-Johnson said. She was there seven days a week.

The museum door was boarded up in preparation for Tropical Storm Barry, and mourners left flowers outside, with a sign reading "Going to miss u."

Roberts-Joseph started the museum with the collection of a former teacher in the East Baton Rouge Parish, later adding exhibits on African art, inventions of black Americans and more, according to The Advocate, a local paper.

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

Then there were the community centers at which Roberts-Joseph worked, spearheading food banks and clothing drives, her sister recalled. There was CADAV, where she served for years as president before passing the job to a younger relative.

Roberts-Joseph may have met celebrities through her work but stayed humble, Armstrong-Joseph said, and always tried to marshal aid for those less fortunate.

"She sought resources that were greater than hers to help those that were in need," Armstrong-Joseph said. "She never met a stranger. I don't care who you were, you were the same in her eyesight."

Armstrong-Johnson last saw her sister when she came over about 10:30 a.m. Friday to bake bread. Her oven was broken, Armstrong-Johnson said.

Roberts-Joseph left for appointments, Armstrong-Johnson said, and never came back.

"Needless to say, the bread is still here," she said.