The police announced an arrest on Tuesday in the killing of Sadie Roberts-Joseph, 75, a beloved community leader in Baton Rouge, La., and the founder of the city’s African-American history museum.

Chief Murphy J. Paul Jr. of the Baton Rouge Police Department said the suspect, Ronn Jermaine Bell, 38, was a tenant in a residence Ms. Roberts-Joseph owned. He was behind on his rent, though it was not clear if that was connected to the killing. The motive was still under investigation, Chief Paul said.

Mr. Bell was charged with first-degree murder. The authorities said he was a registered sex offender who had served time in prison for sexual battery of a child. They did not reveal how they found him, but they said they received many tips from the community.

“There were so many leads; there were so many people who wanted to help bring closure and bring an arrest,” Mayor Sharon Weston Broome of Baton Rouge said at a news conference with law enforcement officials on Tuesday.