The FBI is asking residents in North Dakota and Montana to help find the body of missing Montana teacher Sherry Arnold.
The 43-year-old wife and mother was last seen on a morning run more than a week ago.
"Based on investigative evidence gathered over the last few days, it is believed that Ms. Arnold may be deceased; her body has not been recovered," the FBI said in a statement Sunday.
The agency asked property owners in North Dakota and northeastern Montana to check their land for disturbed soil, and to contact law enforcement if they see anything usual.
Two men are in custody in connection to the investigation.
Lester Waters and Michael Spell are being held in Williams County, North Dakota, on charges of aggravated kidnapping, Williams Country Sheriff's deputy Steve Thompson said.
Arnold's disappearance rocked Sidney, a small town in eastern Montana, about 100 miles south of the Canadian border.
A massive search effort involved hundreds of volunteers, as well as law enforcement authorities and National Guard members.
"We're such a small community and crime is absolutely unheard of," said Christine Mullen, 26, who joined the search effort, even though she didn't know Arnold personally. "We don't lock our car doors. (We're) completely shocked."
Last week, the victim's husband, Gary Arnold, said he was hopeful even as he admitted that the disappearance has been "very difficult" on the couple's children.
He said that he couldn't fathom why anyone "would harm her in any way."
"She is a good person. She's kind, she's sincere," Arnold said of his wife. "She's a great teacher, a referee; she's a great wife and mother."
In an unrelated case, authorities in Hot Springs, South Dakota, were looking for another missing woman.
Constance Beyer, 58, disappeared early Sunday morning from a truck stop when she went to use the restroom.
The case "has no relation" to the Arnold case, said Deputy Jason Wood of the Fall River County Sheriffs' office.