Baton Rouge police have arrested a suspect in the murder of Sadie Roberts-Joseph, a local activist who was found dead in her trunk last week. The suspect, Ronn Germaine Bell, was a tenant in one of Roberts-Joseph's rental homes who was behind on his rent, police announced Tuesday.

A motive is still under investigation, but the killing is not considered a hate crime or tied to Roberts-Joseph's activism. Police said Bell was several months behind on his rent and owed about $1,200. Bell has been charged with first-degree murder.

"All my mother ever wanted was for this community to come together," Roberts-Joseph's daughter Angela said in a news conference Tuesday. "It's ironic that that happened in death. What she wanted to happen in life came to fruition in death."

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An autopsy conducted by the East Baton Rouge Parish Coroner's Office said the preliminary cause of death for Roberts-Joseph, who was 75, was "traumatic asphyxia, including suffocation." Her body found in the trunk of a car on Friday afternoon, about three miles from her home. Police said the 911 calls that led to her body being discovered came from "concerned citizens" who have been cleared as suspects.

This 2004 image shows Sadie Roberts-Joseph. Arthur D. Lauck via AP

Roberts-Joseph founded the Odell S. Williams Now and Then African American Museum, now known as the Baton Rouge African-American Museum.

The discovery left her brother Joseph Armstrong in shock. "We've never seen anything like this in our immediate family. It is really really hard," Armstrong told "CBS Evening News."

"They popped the trunk and she was in the trunk of the car," he added. "How did it happen... or why? Was it a robbery or what?"