He was arrested on Sunday at a Mississippi truck stop on suspicion of kidnapping 12-year-old Lexis Roberts, whose body was found in Louisiana in October.
The remains of a woman believed to be her mother was found in Arizona on Monday. The mother, 31-year-old Suellen Roberts, also had been reported missing from Las Vegas in September.
"There will be an autopsy in the next day or two to verify it was Suellen and possibly give us a time of death," Yavapai County Sheriff's spokesman Dwight D'Evelyn said. "We do believe it is Suellen based on evidence obtained at the scene."
Police began looking for Sanders after he was caught on videotape buying ammunition in Las Vegas on Sept. 3. Authorities said the bullets he bought were consistent with the weapon used to kill Lexis Roberts.
Sanders had an initial appearance Monday in U.S. District Court in Gulfport on a federal kidnapping charge and waived his rights to hearings in Mississippi, said Melanie Rube, a deputy U.S. Marshal. The Marshals Service has 10 days to send Sanders to Louisiana, where the federal kidnapping charge originated. Sanders did not enter a plea during the brief hearing, Rube said.
Detectives said Sanders has lived in Mississippi, Louisiana, Tennessee, Georgia and Nevada.
Some wonder how a man pronounced dead can go unnoticed for so long even though he had been arrested several times under his real name for drug possession and traffic violations.
An official in Lousiana said that it is possible because there is no national death database in the United States. Sanders also wasn't collecting Social Security, so no red flags were raised.
The Associated Press Contributed to this report.