POTOSI, Mo. ? A man arrested after two missing boys were found in his apartment terrorized one of them with a handgun to get him to cooperate, prosecutors allege in new charges filed Wednesday.

Pizzeria worker Michael Devlin was charged with kidnapping Shawn Hornbeck, 15, who had been missing more than four years when he was found Friday. Devlin already had been charged with kidnapping Ben Ownby, a 13-year-old who had been missing four days when he was found with Shawn.

Devlin also is under investigation in the 1991 disappearance of another Missouri boy who still has not been found, The Associated Press has learned.

Michael Devlin is the “most viable lead” in the case of Charles Arlin Henderson, who was 11 when he disappeared in 1991 and has never been found, Lincoln County sheriff’s deputies said.

Washington County, Mo., prosecutor John Rupp said in a statement that Devlin, 41, was charged with kidnapping and armed criminal action. The statement does not name Shawn, but uses the initials SDH.

A probable cause statement released by Rupp said Devlin “abducted SDH utilizing force for the purpose of terrorizing the victim. After securing SDH, Michael Devlin flourished a handgun in order to gain compliance of the minor child. Michael Devlin then transported him out of the county and concealed his whereabouts for four years and three months.”

Rupp and Sheriff Kevin Schroeder would not discuss evidence in the case beyond the probable cause statement, but Rupp said he wanted to shoot down speculation that Shawn ran away on his own.

“Shawn was abducted against his will,” Rupp said. “Period. End of story.”

Devlin, who is being held on $1 million bail, faces arraignment today in the Jan. 8 kidnapping of Ben, of Beaufort, Mo. Shawn, of Richwoods, was abducted Oct. 6, 2002. Both boys were found Friday at Devlin’s apartment in the St. Louis suburb of Kirkwood.

Charles Arlin Henderson, known as Arlin, was, like Ben and Shawn, about 100 pounds and from a rural town about an hour from St. Louis. Both Shawn and Arlin vanished at age 11 while riding their bikes.

“If you were to take a photo of Arlin Henderson and you place it next to Shawn’s picture, there is a striking resemblance,” Lincoln County sheriff’s Lt. Rick Harrell said.

Investigators began re-examining the 1991 case after Devlin’s arrest.