Wallace confessed to killing 10 young women. He was convicted for nine, and now sits on death row.
Detectives and one family told Eyewitness News, they believe there may be more victims.
"It's always been difficult, not knowing what happened to her," said April Maxwell.
April Maxwell's life changed forever 22 years ago -- the day her mother Rita Maxwell walked out of her home in west Charlotte.
"After church she took a stroll, and we never did see her again," said sister Lisa Maxwell Willis.
Willis knew her sister had been living on the edge, on drugs and on the streets.
It was 1992, the same year Wallace had quietly begun what would become Charlotte's biggest killing spree.
Two years later, Wallace would confess to killing 10 young women. Rita Maxwell was not one of them, but her family wonders if she might have been No. 11.
"I later found out that she did know him because we had him investigated," Willis said.
"I know that he said that he knew her but he didn't do anything to her," said daughter Kristie Maxwell.
They're not the only ones wondering if Wallace was telling the truth.
Bill Ward was the lead detective on the Wallace investigation. He's now with Charlotte-Mecklenburg Police Department's cold case squad and has always believed that Wallace had killed more women, including possibly Rita Maxwell.
"In my heart, I believe there are other victims here," Ward said.
Months after Wallace was taken to death row for killing nine women, Ward went to Central Prison to ask about others.
"But he had other ideas. He wasn't willing to talk with us and cooperate," Ward said. "The idea is we still want information on these, and it's something we do care about and we want people to respond."
Rita Maxwell is one of about 30 missing people on the department's website and Detective Lee Tuttle has started collecting DNA samples from family members to help identify possible victims, including, perhaps, Rita Maxwell.
"It's a big deal to the families, too, because this is something they've struggled with for years," Tuttle said.
After all that time, Willis can't even be sure that her sister is dead and if she is that Wallace killed her. She and her family haven't stopped praying.
"We pray that if he did do it that he would confess, because 22 years has gone by and not knowing is the worst thing ever. What happened to my sister, their mother?" Willis said.
Wallace may be the only one who can say what happened to Rita Maxwell, but his attorney denied Channel 9's request for an interview.
Wallace remains on death row with no date set for his execution.