Louisiana authorities have arrested a man in the murder of activist Sadie Roberts-Joseph, the founder of Baton Rouge's only African-American history museum.

Ronn Bell, 38, was arrested and charged Tuesday with first-degree murder in Roberts-Joseph's death.

Roberts-Joseph, 75, was last seen visiting her sister at 11 a.m. Friday. She was found dead in the trunk of a car at 3:45 p.m. about 3 miles from her home, the Advocate reported.

A preliminary autopsy conducted by the East Baton Rouge Parish Coroner's Office determined that Roberts-Joseph's death was caused by "traumatic asphyxia."

Her death, Baton Rouge police said, is not being treated as a hate crime.

"There's no information which leads us to believe this incident was motivated by her activism or her community efforts," said Baton Rouge police chief Murphy Paul at a press conference held Tuesday.

Police did not suggest a motive but did say Bell lived in one of Roberts-Joseph's properties and was several months behind on his rent.

Bell is a registered sex offender, have pleaded guilty in 2007 to the sexual battery of an 8-year-old.

Police did not say whether Roberts-Joseph was aware of Bell's role as an activist.

Contributing: Follow Joshua Bote at @joshua_bote;