MANCHESTER — At first, Peter Mars didn’t believe what he was seeing through the drive-through window at his bank.

“I see this guy in a ski mask jumping back and forth and waving what appeared to be a semi-automatic handgun. I could tell he was ordering them to give him all the money,” Mars said. “I thought, is this a movie or what?”

It was indeed a robbery. One that Mars, an off-duty Franklin County sheriff’s deputy, helped to foil Monday after he pursued the suspect in a high-speed chase that ended with the arrest of an Augusta man.

After seeing the robbery from the drive-through window, Mars and his son, a former police officer, followed the suspect in their car until Kennebec County sheriff’s deputies could join in the chase.

At times the chase surpassed 100 mph, but Mars maintained contact long enough for deputies to make the arrest.

Jonathan C. Linton, 36, of Augusta was charged with robbery in the holdup at the Savings Bank of Maine branch in Manchester, said Sheriff Randall Liberty.

While reporting a robbery to emergency dispatchers, Mars followed Linton’s white sport utility vehicle as it raced away from the bank. He told dispatchers minor details, such as the temporary paper plates on the vehicle, and began giving a play-by-play of the chase.

The SUV pulled into a veterinary hospital on Route 202 and backed out before passing Mars, who had pulled over to the side of the road.

Mars was in his personal vehicle without an emergency light.

As the SUV approached 100 mph, it looked like the driver was going to lose control. “He just made it around the corner,” Mars said, referring to one serious scare. “I thought he was going to roll it.”

As the speed and the traffic started to pick up, Mars handed the phone over to his 42-year-old son, David, who worked for a time as a patrolman with the New York City Police Department.

“He was great, he was on that cell phone and he was giving the 911 dispatcher every move,” said Mars.

The SUV turned east onto Route 135 and the suspect suddenly pulled into a driveway and stepped from the car without the mask.

Mars said he reported the suspect’s description to dispatchers and, because he was unarmed, decided to keep his distance and avoid a confrontation.

After briefly losing sight of the SUV, Mars saw Kennebec County Sheriff’s Capt. Dan Davies handcuffing the suspect on the side of Prescott Road.

The chase continued for roughly 15 miles, Mars said.

It would have been difficult to make the arrest so soon without the immediate pursuit and Mars’s “play-by-play,” said Liberty.

Mars helped to keep a “dangerous man” off the streets, he said.

Franklin County Sheriff Dennis Pike commended his deputy for showing “great judgment” and “restraint.”

Mars declined to give his age, but said he is in his 60s. He is the first chaplain for the Franklin County Sheriff’s Office, Pike said.

With 44 years in law enforcement, Mars deflected credit. “Talk about being in the right place at the right time,” he said. “How many times are you going to come across something like this?”