(CNN) Activist Sadie Roberts-Joseph 's alleged killer was likely a tenant in one of her rental homes and behind about $1,200 on his rent, Baton Rouge Police Chief Murphy Paul said Tuesday.

The chief emphasized investigators believe Ronn Jermaine Bell killed Roberts-Joseph but they have yet to establish "a complete, solid motive at this time."

Bell, 38, who is a convicted sex offender, has been charged with first-degree murder, Paul said. Bell was initially arrested Monday on a warrant for failing to register as a sex offender, according to authorities.

Bell's sex offender status stems from a guilty plea Bell entered in 2007 in a sexual battery case after he was accused of the aggravated rape of an 8-year-old girl in 2004, East Baton Rouge District Attorney Hillar C. Moore, III, told reporters. Bell served seven years in prison, Moore said.

The arrest came after Paul expressed confidence that someone would apprehended in the case of the community stalwart and museum founder who was found dead in the trunk of her car last week

Paul said phone calls poured in from the community and family members gave police leads since the killing.

"Thank you, Baton Rouge, thank you for caring," Paul said.

The East Baton Rouge Parish Coroner's Office had determined the preliminary cause of death was "traumatic asphyxia, including suffocation."

Roberts-Joseph, 75, did not die by strangulation, coroner Beau Clark told CNN. Her nose and mouth were blocked, he said without elaborating.

A toxicology report will be available in three weeks, Clark said.

"All my mother ever wanted was for this community to come together. It's ironic that that happened in death," Roberts-Joseph's daughter, Angela Machen, told reporters. "What she wanted to happen in life came to fruition in death. However, we will see to it that her legacy continues."

She wanted to unite the community

The Baton Rouge community came together Tuesday for a vigil at the Odell S. Williams Now and Then African American Museum, which Roberts-Joseph founded in 2001. Together, they sang and praised God, the police and one another for finding the man accused of taking the leader from the community.

They also prayed for the suspect, saying that he and his family were also struggling.

Pastors, community leaders and Roberts-Joseph's family members urged those remembering her life to continue her mission of teaching people their own history and creating a safer, more unified community.

"She let her work speak for her. When you look at this crowd, the number of people out here today, don't you hear Sadie?" Roberts-Joseph's friend, 100-year-old Johnny Jones told the audience. "They're all speaking for her."

Roberts-Joseph hosted the city's Juneteenth festivities, which celebrate the last slaves in the Confederate states learning of their independence more than two years after the Emancipation Proclamation was signed, at the museum every year.

She also founded Community Against Drugs and Violence, a non-profit organization focused on creating a safer environment for children in north Baton Rouge.

"Her motto was roll up your sleeves and get the job done. So, in closing, I say to you: roll up your sleeves and get the job done," said Reverend Reginald Pitcher.

Her family saw her earlier that day

Roberts-Joseph's body was recovered about 3:45 p.m. Friday after an anonymous caller reported finding her, according to Baton Rouge police spokesman Sgt. Don Coppola.

The car was located behind a vacant home, Paul said. Two residents who reported the body in the car have been cleared as suspects, the chief said.

Her family had seen her earlier that day, Coppola said. She had been making cornbread with her sister, according to her niece, Pat LeDuff.

Sadie Roberts-Joseph

Roberts-Joseph's car was found about three miles from her home, Baton Rouge police said.

Bell, who was about two months behind on his rent, had intended to contact Roberts-Joseph on the day of her death, according to an affidavit for an arrest warrant.

Surveillance video captured Bell leaving the area where Roberts-Joseph's body and car was found. He admitted to being there and at the same time the car was abandoned. But Bell said he was not in the vehicle, the affidavit said.

A witness told police someone fitting Bell's description was seen abandoning the car and walking away, according to the police record.

Bell told police he didn't see Roberts-Joseph on the day she was killed and hadn't seen her for several days.

Bell's DNA was found on Roberts-Joseph's body, the affidavit said.

Roberts-Joseph extended Bell grace with the past due rent.

She told him he could stay at the home as long as he paid her some money, he told police.

Roberts-Joseph's son, Jason Roberts, told CNN affiliate WBRZ his mother's life should not have ended the way it did.

His message to her killer: "You stole light. You stole a warm, loving, giving and caring woman. And it wasn't just for her family. She cared for the city. She cared for you. She would want forgiveness for you."