WATERVILLE — A Skowhegan man on federal probation for robbery was arrested Monday night off Main Street after an officer stopped him for driving without headlights and noticed he had a gun in his back pocket.

Raymond Ellis Jr., 30, was charged with possession of a firearm by a prohibited person — a felon — and taken to Kennebec County jail in Augusta where his bail was $5,000 cash, according to Waterville Deputy police Chief Bill Bonney.

Bonney said Tuesday that the incident illustrates how law enforcement officials never know what they will face during what may appear to be a routine traffic stop. In this case, Officer Paul Heath seized the firearm and, fortunately, Ellis was cooperative, Bonney said Monday.

Around 8:40 p.m. Monday, Bonney said, Heath saw a black sport utility vehicle operating without its headlights on Main Street. He stopped it in the parking lot of Railroad Square and identified the driver as Ellis. During a routine check, Heath noticed Ellis was on federal probation for a weapons charge, according to Bonney.

“Through further investigation, Paul learned that Mr. Ellis was on federal probation for robbery,” he said. “The officer continued to investigate and talked to Ellis, got Ellis out of the car and … noticed a metal object protruding from his back pocket and immediately recognized it as a firearm.”

Heath then arrested Ellis and charged him with possession of a firearm by a prohibited person, a Class C felony punishable by up to five years in prison, according to Bonney.

Ellis is scheduled to appear in court at 8:30 a.m. Feb. 24 at the Capital Judicial Center in Augusta, he said.

Reflecting on a case that occurred Dec. 22 in which Waterville police Officer Timothy Hinton was shot twice during a traffic stop after a report of a shoplifter, Bonney said Monday’s incident shows that officers never know what they will face when doing what may appear to be a routine stop.

“It just illustrates what our officers are dealing with on a daily basis,” he said.

Ellis was still at the jail as of 2:15 p.m. Tuesday, a spokesman there confirmed.