A Louisiana man has been arrested for the murder of a beloved 75-year-old community activist whose body was discovered asphyxiated in the trunk of her car, police said at a news conference Tuesday afternoon.

The death of Sadie Roberts-Joseph, who founded an African American museum in Baton Rouge and teamed up with police on an anti-drug and violence program, was ruled a homicide by «traumatic asphyxia, including suffocation,» according to an autopsy report.

Ronn Jermaine Bell was taken into custody Tuesday on a charge of first-degree murder, police said.

Bell was living in one of the homes Roberts-Joseph was renting out and it is believed he was several months behind in rent payments, police said. Authorities estimated Bell owed Sadie-Joseph $1,200.

Roberts Joseph was found slain Friday afternoon when police were directed to her car parked in a residential neighborhood northeast of downtown Baton Rouge, police said.

«It is with great sadness and respect to investigate any unexpected or traumatic death. When our investigation involved an innocent victim, such as Ms. Sadie Joseph, it is particularly tragic,» Dr. William «Beau» Clark, the East Baton Rouge Parish Coroner, said in a statement on Friday.

PHOTO: Sadie Roberts-Joseph is interviewed by WBRZ. WBRZ
Sadie Roberts-Joseph is interviewed by WBRZ.

«She’s special. She’s touched so many people in this community over the years. She was a true public servant,» Baton Rouge Police Chief Murphy Paul told ABC News.

Roberts-Joseph was last seen alive visiting her sister about 11 a.m. on Friday. Her body was discovered in her car a little over three miles from her home about 3:45 p.m. on Friday, police and relatives said.

There was a 90 minute time frame that investigators focused on, from the time she was last seen alive to the time her body was found, police said.

A warrant was already issued for Bell on unrelated charges including failing to comply, probation regulations and failing to register as a sex offender.

Bell was previously convicted for sexual assault against an 8-year-old girl, police said, adding Bell pleaded guilty in 2007 to sexual battery and received a seven year sentence, which was completely served.

The slaying of Roberts-Joseph, who was well known in Baton Rouge, came as a complete shock for her family and the community.

«We’re devastated that someone has actually killed her and put her in the trunk of her own car,» Roberts-Joseph’s niece, Pat McCallister-Leduff, told ABC News.

The victim’s sister, Beatrice Johnson, told The Advocate newspaper of Baton Rouge that Roberts-Johnson stopped by her house around 11 a.m. on Friday. She said her sister lived near her in the Scotlandville neighborhood of Baton Rouge and would check in with her daily.

«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,» Johnson told the newspaper. «The bread is still there. She never came back to get it.»

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 housed on the campus of New St. Luke Baptist Church in Baton Rouge.

She also organized the city’s annual Juneteenth festival at the museum, commemorating the day slaves were belatedly freed in Texas more than two years after Emancipation Proclamation was signed. She also partnered with Baton Rouge police to launch a Community Against Drugs and Violence program.

In a recent interview with ABC affiliate station WBRZ in Baton Rouge, Roberts-Joseph said her work at the museum and the annual Juneteenth event was meant «to celebrate, to embrace» African American history and to «learn of our past and to be able to move forward in unity.»

Baton Rouge police are asking anyone with information on the case to contact homicide detectives immediately.

«I have no idea why someone would do such a heinous act or commit such a heinous act for someone who had nothing but love for this community and love for people,» Baton Rouge Mayor Sharon Weston Broome told ABC News.