York explained the details of the incident that merited the suspension during Monday's meeting of the board.
The incident took place in late January, when Arnold responded to a request for assistance from another officer with regard to an encounter with a man who, according to York, was in a delusional state, to the degree where the man was not wearing shoes on a frigid day.
The man was resisting officers to the point where he got into a police vehicle and put it into gear, but did not cross the line into violent resistance against officers, according to York. However, the man was admitted to a local hospital with injuries that required medical treatment, and the hospital notified the police department to that effect.
An internal investigation was initiated, with video from the squad cars and assessment from police training instructors ultimately indicating that Arnold used excessive force, with the man sustaining, according to York, at least one "non-displaced fracture of his jaw." York said Arnold used multiple strikes to the man's head.
"Obviously, this is a very serious situation," York said, who also said that "I think the 30-day suspension is the right way to go."
York explained that the suspension and investigation, which was aided by the placement of cameras in squad cars, is the proper result of modern policing, because officers have to correctly determine how to respond to situations and have to be held accountable when excessive force is used.
"The degree of resistance is important," York said. "This person...he wasn't attacking officers. We train officers for a reason, where we say 'This is the way we want to handle a situation.'"
Arnold's suspension led to York presenting to the Board of Public Safety a potential rule change that will be finalized for the Sept. 9 meeting, where the definition of "unreasonable" and "excessive" force will be clarified, with instances of excessive force going straight to the board for disciplinary action up to and including potential termination of employment.
Arnold, who joined the force in October 2007, has four previous suspensions on his record as well as a letter of reprimand, with four of those instances prompted by police vehicle accidents, according to the police department.
York said Arnold will also spend time in remedial training at the Public Safety Academy at the end of the suspension, likely for a week.