Updated

For nearly two decades, a Mississippi man legally declared dead openly used his real name even when he was arrested on drug, battery and other charges. Now, Thomas Steven Sanders, who went unnoticed by authorities for so long, is behind bars again, accused of kidnapping a Las Vegas girl who turned up dead and a possible suspect in the disappearance and death of her mother.

Sanders is charged with kidnapping 12-year-old Lexis Roberts, whose body was found last month in Louisiana, the FBI said. Remains found Monday along a remote mountainous stretch of Interstate 40 in northwestern Arizona are likely those of the girl's mother — 31-year-old Suellen Roberts — who also had been missing, the Yavapai County Sheriff's Office said.

"We do believe it is Suellen," Yavapai County Sheriff's spokesman Dwight D'Evelyn said. An autopsy in the next day or two will verify it is the woman and possible time of death, he said.

The bizarre case leaves many wondering how a legally dead man can go unnoticed by authorities for so long — even after being arrested in several states under his real name. His latest arrest came after someone tipped off authorities. He was picked up Sunday at a Gulfport, Miss., truck stop after a nationwide manhunt that started when he became the suspect in Lexis' kidnapping.

Authorities say the answer to how Sanders stayed under the radar is pretty simple. There's no national death database in the United States, said James Kelly, sheriff of Catahoula Parish in central Louisiana where the girl's skeleton was found by hunters in woods off a dirt road Oct. 8.

And at age 53, Sanders wasn't collecting Social Security, raising no red flags. It's not even clear if Sanders knew he was considered dead.

"Right now we have a lot more questions than we do answers," Kelly said earlier Monday, adding Sanders was cooperating with investigators.

Sanders had met Roberts and her daughter a few months ago. The trio had been spotted at a drive-thru wildlife park in Williams, Ariz., and at the Grand Canyon over Labor Day weekend, authorities said.

Roberts and her daughter were reported missing from the Las Vegas area in September.

Sanders had an initial appearance Monday in U.S. District Court in Gulfport on the 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.

The public defender appointed for him did not return a message.

Much of Sanders' past is a mystery ever since he walked out on his family in McComb, Miss., in 1987. He drifted from state to state and didn't buy property or establish many bills in his name — things that create a paper trail for most people, authorities said.

His wife, Candice Sanders, divorced him in 1988 for allegedly "habitual, cruel and inhuman treatment."

Years later, Sanders' parents, brother and ex-wife petitioned a Mississippi court to have him declared dead. That was in July 1994, apparently so his children could receive death benefits, but it's not clear if they did. The Social Security Administration said privacy laws prohibit the agency from discussing death benefits. Kelly said he didn't think the family received such benefits.

Sanders moved around the country using his real name, though authorities said he sometimes gave his name as Tom or Steve or the nickname "Spider." Investigators know he lived in Mississippi, Louisiana, Tennessee, Georgia and Nevada. He worked as a laborer, a welder and a scrap metal collector.

He was arrested several times, on charges including possession of drug paraphernalia and for several traffic and motor vehicle violations in Tennessee, according to authorities. He also was sentenced to two years in Georgia for simple battery. State and federal authorities said some of the charges involved minors, but they haven't elaborated.

In Nevada, Sanders met Roberts and her daughter Lexis a few months ago at a storage facility where Roberts kept some possessions and where Sanders worked for a time, Roberts' mother Mary Woodburn has told The Las Vegas Review-Journal.

Officials said security cameras showed Sanders buying ammunition Sept. 3 at a Walmart in Las Vegas. The bullets he bought were consistent with the weapon used to kill Lexis, authorities said.

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Associated Press Writer Felicia Fonseca in Phoenix contributed to this report.