Montana teacher found dead, 1 in custody January 13, 2012 -- Updated 1842 GMT (0242 HKT) Sidney Public Schools says it learned Sherry Arnold was dead on Friday morning The FBI says a man is in custody and another "is being questioned" in her case Arnold was last seen six days ago while out on a morning run (CNN) -- A 43-year-old Montana schoolteacher last seen six days ago while out on a morning jog has been found dead, her school said Friday. Sidney Public Schools, where Sherry Arnold had worked as a math teacher at Sidney High School, announced on its website 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. Arnold went running around 6:30 a.m. last Saturday around her small town in eastern Montana but never returned home. Other than one of her running shoes that was found along her route, authorities had not indicated -- until Friday -- that there's been any sign of her.