A Douglas County sheriff’s deputy had a split second to react Friday when he suddenly came face to face with a man holding an assault rifle near an SUV stopped along a suburban roadway.

The sheriff’s office on Wednesday released video of Deputy Brad Proux, a six-year veteran, approaching the vehicle and suddenly encountering the driver, who stood with an assault rifle in his hands.

Proux shot Deyon Marcus Rivas-Maestas, 25, who has been charged with first-degree assault of a peace officer, said Littleton Police Department Chief Doug Stephens.

Investigators do not know why Rivas-Maestas stepped out of the SUV with the rifle in his hands, or why he was stopped on the roadside. The gun was not loaded, Stephens said.

Stephens called Proux a hero for his quick reaction and his calm, professional handling of the situation after he hit Rivas-Maestas in the arm with one bullet. Proux held Rivas-Maestas at gunpoint for four minutes until back-up officers arrived, Douglas County Sheriff’s Chief Deputy Steven Johnson said.

Proux had stopped about 6:45 p.m. Friday on County Line Road just east of Santa Fe Drive in an area of Littleton that is in Douglas County, police said. The deputy had seen the SUV on the roadside and decided to make a courtesy stop to help what appeared to be a stranded motorist.

The Douglas County sheriff’s office released footage from Proux’s body camera, saying it was a prime example of how a routine stop can turn dangerous in an instant and that the footage illustrates the quick decisions law enforcement personnel often are forced to make.

“This incident occurred very, very quickly,” Johnson said. “I speak for every law enforcement officer: When you hear ‘Shots fired. Shots fired,’ it’s the worst thing that can happen.”

The initial encounter between the two men was so brief that it’s nearly impossible for the casual viewer to notice the rifle in Rivas-Maestas’ hands. The video shows Proux firing two quick shots and falling down as Rivas-Maestas scrambles to get away.

“Deputy Proux — amazing,” Johnson said. “It’s nothing more than amazing that he was able to defend himself.”

Proux, who was not injured, remains on administrative leave. He has told supervisors that he feels ready to return to work, Johnson said.

Rivas-Maestas suffered a gunshot wound to his arm and underwent surgery. He was released from a local hospital Wednesday afternoon and was being booked into the Douglas County jail, Stephens said.