(CBS/KTVQ/AP) SIDNEY, Mont. - The FBI has joined the search for missing Montana teacher Sherry Arnold. An FBI spokesperson says because of the abduction potential and the proximity of North Dakota, agents are on the ground in Sidney.
CBS affiliate KTVQ reports the search for Arnold is in its third day. A small team of law enforcement officers and firefighters combed rural areas outside the town, trying to uncover clues as to what happened.
Authorities say they will search one more day for the 43-year-old Arnold, who left her home for a pre-dawn run and never returned.
A single shoe in a ditch is all that's been found of her since Saturday morning.
Sidney Mayor Bret Smelser says search teams Tuesday will re-canvass surrounding areas, looking for any more clues. After that, searches will be based on leads developed by police and FBI agents.
MSNBC reports no solid evidence has emerged to indicate that she was kidnapped, authorities said.
"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."
Snow and rain is expected Tuesday and temperatures are expected to drop into the teens overnight.
Hundreds of volunteers have helped in the search for the missing teacher. Sherry's older sister Rhonda Whited Rupp says her family is still in shock over her sister's disappearance in the small, tight-knit community.
Sherry and her husband, Gary Arnold, had five children from previous marriages, including two still living at home and attending Sidney High School, Whited said. Colleagues described her as a devoted teacher.
Police are asking anyone with information about the whereabouts of Sherry Arnold to call the Sidney Police Department at 433-2210. You can also call the Richland County Tipline at 406-433-4027.