Her body was found Tuesday, Jan. 17.
The two men were detained after a tip to a hotline set up by authorities regarding Arnold’s disappearance.
Arnold, 43, was last seen setting off for a run on Saturday, Jan. 7, in Sidney, a fast-growing agricultural community in northeastern Montana; her husband, Gary Arnold, reported her missing when she did not return home.
Searchers found one of Arnold’s running shoes, a few days after her disappearance, on the outskirts of Sidney, which has undergone rapid growth amid a regional oil and gas boom.
Bret Smelser, the mayor of Sidney, told Reuters that the crime has shattered the sense of security in the community of 5,000 people, where new homes were being built amid rapid growth brought on by a boom in oil and natural gas extraction through hydraulic fracturing.
"We never think it will happen in a small town. Now it has and we have to deal with it," he told Reuters.