A task force of federal, state and local investigators will examine whether the man accused of abducting two boys may have snatched other children who are still missing.
Michael Devlin is charged with kidnapping two boys found Jan. 12 in his apartment.
The search for Ben Ownby, who vanished after getting off a school bus on Jan. 8, led police to Devlin's home, where they found the 13-year-old and Shawn Hornbeck, who had been missing for more than four years.
Several experts and police have called it unlikely that someone would commit such brazen crimes without any precedent. Devlin was 36 when Shawn was abducted on Oct. 6, 2002.
"There are the possibilities that there may be other kids involved," Franklin County Sheriff Gary Toelke said.
Authorities are looking into the cases of two boys and one girl who disappeared from towns on the outskirts of St. Louis dating back to 1988.
One detective called Devlin the "most viable lead" in another missing boy case, mostly because of striking similarities between Shawn's abduction and that of 11-year-old Charles "Arlin" Henderson, who vanished in 1991, the AP says.
Lincoln County detective Chris Bartlett said the boys were the same age when they vanished and both were taken while riding their bikes on rural roads about an hour's drive from St. Louis. Shawn, Ben and Arlin all weighed about 100 pounds.
Devlin's attorney, Ethan Corlija, did not return messages seeking comment on Friday.
Shawn's parents appeared Friday on several morning television shows. On NBC's "Today" show, the boy's stepfather, Craig Akers, said Shawn was surprised to find his room virtually the same as when he had last seen it.
"Believe it or not, there was one T-shirt in that drawer that did fit him," Akers said. "He was just tickled pink that everything was just the way it was left."