BILLINGS, Mont. — Authorities expanded their search Monday for a high school teacher who's missing from an oil boom town in northeast Montana, after recovering only a single running shoe since she failed to return from a weekend run.
No solid evidence has emerged to indicate 43-year-old Sherry Arnold was kidnapped, authorities said. But FBI agents were called in to assist local law enforcement in the case, and an agency spokeswoman said the possibility of abduction was under investigation.
The search for Arnold was focused on a 10-square-mile area north of the town of Sidney near the North Dakota border. That's in the general vicinity of the roadside ditch where Arnold's shoe was discovered Saturday along one of her running routes.
Her family confirmed the shoe was hers, said Sidney Assistant Police Chief Robert Burnison.
"It's just been grueling," said Arnold's father, Ron Whited, who runs a ranch outside of Sidney. "When you can't find someone and you do find a shoe and you know that's where she was running, something obviously wasn't right. I can tell you I would never believe I would be looking for my daughter."
Arnold, who grew up in Sidney and returned there to teach after college, left her home for an hour-long run at about 6:30 a.m. Saturday, Whited said. Her family reported her missing after she failed to return.
A witness reported seeing someone matching the missing woman's description that morning near where the shoe was found, but no clues have been found since, Burnison said.
An automated tip line has been established by local authorities to collect information on the case: 406-433-4027. Whited said the family had considered posting a reward for information but was holding off on the advice of law enforcement.
Arnold's disappearance comes amid turbulent times in Sidney, where a boom in the nearby Bakken oil fields of eastern Montana and western North Dakota has swelled the town's population from about 5,000 people several years ago to more than 6,000 today, officials said.
Mayor Bret Smelser, who attends church with Arnold's parents, said she is "a daughter of the community" whose disappearance brought out the best in hundreds of residents from Sidney and surrounding towns who have participated in the search.
Colleagues described Arnold was a mother and devoted algebra teacher who has taught in the Sidney system for 18 years. Her husband, Gary Arnold, works in the school district's administrative offices as director of federal programs.
"She's one of those teachers that every parent wants in front of their child," said Sidney Schools superintendent Daniel Farr. "She's there early in the mornings and she's there after school. She is just a generous and caring person."
Sherry and Gary Arnold had five children from prior marriages, including two still living at home and attending Sidney High School, Whited said.
Hundreds of people, most of them volunteers, turned out for the search over the weekend. National Guard troops, a helicopter, several airplanes and canine search teams also took part in the search.
Volunteers were told Sunday they would be contacted if more searchers were needed. But Burnison said about 50 showed up anyway Monday to help about 100 to 120 law enforcement officers, police and others involved in the effort.
The FBI was asked to help because of the agency's expertise and resources, Burnison said.
FBI spokeswoman Deborah Bertram said there was a second reason, too: Sidney is just a few miles from the North Dakota border, so any abduction that took Arnold across state lines would make it a federal case.
The search was to resume Tuesday morning but might be suspended at the end of the day if no other clues in Arnold's disappearance are found, Burnison said. But he said the investigation would continue.
Mayor Smelser said the outpouring of volunteers showed Sidney has remained a tight-knit community despite the changes brought by a massive influx of oil field workers in recent years.
"My big fear as mayor is that we'll lose our small town charm and personality with the second wave of oil, but this is the way Sidney has always been. It's an amazing community," he said.
"What we need right now is everybody's prayers," Smelser said of the search. "The window of opportunity is slipping on us."