Ronn Jermaine Bell, 38, was arrested and charged with first-degree murder in the death of Sadie Roberts-Joseph, the Baton Rouge Police Department said at a press conference Tuesday.
Bell was a tenant in one of Roberts-Joseph's homes, and he was behind on rent by about $1,200, police said.
Police also said Bell is a registered sex offender and had served time in prison for the sexual assault of a young girl.
Authorities said they still do not know the motive for Roberts-Joseph's killing.
Roberts-Joseph, 75, was a well-known community leader who worked with law enforcement on programs tackling drug use and gang violence. She was the found and curator of Baton Rouge's African-American museum and had recently organized its annual Juneteenth festival celebrating the date of June 19, 1865, when those enslaved in Texas were finally freed.
Roberts-Joseph was last seen Friday at her sister's house, from whom she lived three doors down.
Her body was found about 3 miles from her home just a few hours after she had been last seen. Her cause of death was "traumatic asphyxia, including suffocation," according to a statement from the coroner's office.