The FBI has joined the search for missing Montana mother and teacher Sherry Arnold and investigators are considering the possibility that Arnold could have been abducted and taken across the nearby North Dakota border.
"In cases where an adult may have been taken across state lines against their will, the FBI becomes involved," Debbie Dujanovic Bertram, the FBI public affairs specialist in Salt Lake City, told ABCNews.com. "We are not saying that happened, but it is one of the angles we are looking into."
The teacher disappeared from her town of Sidney, Mont., which is about 11 miles from the North Dakota state line.
Arnold, 43, disappeared sometime between 6:30 and 6:45 a.m. on Saturday morning, according to police who will not specify how this timeframe was determined.
She is currently considered a missing person and the FBI would not comment on whether they believe foul play was involved or if the case will be soon be classified an abduction. They have not named any suspects at this time.
"We're not ruling anything out at this point," Bertram said. The FBI is jointly investigating with the Sidney Police Department.
Today is likely the last day of a wide-scale search for Arnold, but the investigation will continue.
"We are re-canvassing that area and then will scale back the search and continue in the direction we think we need to go," Bertram said. "It's a matter of making sure we're covering all the ground that we need to cover in the most timely and resourceful way that we can."
So far, the only trace of Arnold that investigators have announced was the discovery of a running shoe identified as Arnold's along a highway route that was part of her usual course.
Arnold's stunned family is praying for her return.
"I'm hoping she's found. I'm hoping that she's healthy. I miss her so badly," Arnold's husband Gary Arnold told ABCNews.com. "We miss her so badly. This community needs her back."
When asked what he thinks may have happened to his wife, Arnold said in a choked voice, "I don't even want to go there at this point."
The couple has five children between them from previous marriages. Gary Arnold has three and Sherry Arnold has two.
She has been a teacher in Sidney since 1993, teaching at both the middle school and high school, where she is currently a math teacher.
"Sherry is one of those teachers that every parent wants in front of their child," Sidney School District Superintendent Daniel Farr told ABCNews.com.
"She is caring, first and foremost, one that is there before and after school helping students," Farr said. "She gets to know her students. She becomes a mentor to many a student that goes on to become a math teacher."
Search and rescue teams have used canine units, private planes, a helicopter, searchers on ATVs and on horseback.
Sidney is a small town of roughly 5,000 people that has experienced a rather sudden influx of out-of-towner oil workers following the Bakken oil boom in North Dakota, according to the Billings Gazette.
Sidney Police Chief Frank DiFonzo told the newspaper that crime rates have gone up since the influx in areas including bar fights, domestic violence and drunk driving.
Arnold has brown eyes and black hair. She is 5 feet, 10 inches tall with a slender build, weighing about 140 pounds. She was last seen wearing a hooded sweatshirt with white stripes on the sleeves, red nylon pants with black leggings and black gloves.
Authorities are asking that anyone with information regarding Arnold's whereabouts please call the Sidney Police Department at 406-433-2210.