- One man, 47, is being held in Arnold's case in North Dakota, a police chief says
- Another man, 22, is being "detained for questioning" in South Dakota, he says
- Sherry Arnold was a teacher with the Sidney Public Schools in eastern Montana
- She had last been seen six days ago out on a morning run
Two people have been detained in the death of a 43-year-old Montana schoolteacher last seen six days ago while out on a morning jog, law enforcement agencies said Friday.
Sidney Public Schools, for which Sherry Arnold had worked as a math teacher at Sidney High School, announced that the school district learned of her death around 9:30 a.m. Friday.
No other details were immediately available.
Law enforcement officers have taken "one adult male into custody, and another adult male is being questioned" in relation to Arnold's case, the FBI said Friday in a statement.
"The investigation to determine what happened to Ms. Arnold continues," the federal agency said.
Sidney Police Chief Frank DiFonzo told reporters later Friday that law enforcement officers in North Dakota -- including members of the Williams County Sheriff's Office, Williston police and the North Dakota Criminal Investigation Bureau -- helped arrest the first man, who is 47 years old.
That man is now being being held in a Williams County, North Dakota, jail.
The second male, age 22, has been "detained for questioning" in Rapid City, South Dakota, added DiFonzo.
The police chief declined to offer further details or answer questions "because this investigation is rapidly moving forward."
Arnold went running around 6:30 a.m. last Saturday in her small town in eastern Montana, but never returned home. Other than one of her running shoes found along her route, authorities had not indicated -- until Friday -- that there had been any sign of her.
The woman's disappearance rocked Sidney, located about 100 miles south of the Canadian border. It has a population of just under 5,200 people, according to the U.S. Census Bureau.
A massive search effort involved hundreds of volunteers, as well as law enforcement authorities and National Guard members. Authorities on Wednesday "determined the prudent course of action is to scale back the ground search."
"We're such a small community, and crime is absolutely unheard of," said Christine Mullen, 26, a CNN iReport contributor who joined the search effort, even though she didn't know Arnold personally. "We don't lock our car doors. (We're) completely shocked."
The FBI said Friday that "dozens of tips were called into (a) tip line" -- one of which led to the arrest and questioning.
Sidney Public Schools said that all sporting events for Friday had been canceled and "additional counselors (were) on hand" to help students cope.
In interviews with HLN's Jane Velez-Mitchell earlier this 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."