After his arrest, Caswell, 28, 121 Walker Lane, Whitesburg, allegedly admitted he'd been using meth for several days.
Shortly before 6:30 p.m. on Saturday, the Hawkins County Sheriff's Office responded to a report of a man walking along the concrete handrails of the High B. Day Bridge on Route 66S just south of Rogersville.
When Deputy Jason Montgomery arrived, he observed the man, later identified as Caswell, and another male at the nearby Creekside Market.
HCSO Chief Deputy Tony Allen told the Times-News on Monday that at that point Caswell wasn't in trouble. He reportedly had an open container of alcohol and may have been intoxicated, but at the most he might have received a citation, Allen said.
But Caswell allegedly gave Montgomery a phony name, and while Montgomery was attempting to verify that name, Caswell fled the scene on foot.
Montgomery reportedly pursued Caswell across Route 66S, through a field and to the riverbank, where Caswell reportedly jumped in and swam away from shore.
Caswell refused orders to return to shore, and eventually the Hawkins County Rescue Squad was dispatched to the scene with a boat.
Rogersville Police Department Officer Cambren Gibson accompanied the Rescue Squad and attempted to pull Caswell into the boat, but Caswell reportedly resisted.
"Patrolman Gibson got into the water to assist, but (Caswell) began to fight and grabbed Patrolman Gibson by the shirt collar and pushed him under the water on two different occasions," Montgomery said.
Gibson then gained control of Caswell and "assisted" him into the boat, where Caswell allegedly continued to fight and resist until he was subdued.
Caswell was charged with two counts of aggravated assault on an officer, evading arrest, criminal impersonation, resisting arrest and public intoxication.
He was being held in the Hawkins County Jail with no bond set pending arraignment Monday in Sessions Court.