A rolling argument between a Robbinsdale undercover officer and a Coon Rapids man escalated into an apparent full-blown case of road rage Thursday.

In the end, the officer was shot. And a suspect, the father of two children who were in his vehicle during the shooting, was jailed.

The Robbinsdale police chief said his officer was just doing his job. But the suspect's family said the plainclothes officer pulled his gun and that the man fired to protect his family.

"This is a case of people letting their tempers get out of control," said Timothy Snell, deputy police chief for Coon Rapids. "It escalated and became a deadly force situation just because of some petty misdemeanor driving issues."

Martin Scott Treptow, 35, of Coon Rapids, was arrested. Police refused to release the 27-year-old officer's name, saying he was working undercover, but he is described as a six-year veteran of the Robbinsdale police force. He sustained injuries to both legs and an arm, although investigators aren't sure how many shots were fired.

The incident was particularly dangerous, Snell said, because the area was crowded with people. Many now are witnesses, he said.

Here is the account Coon Rapids police have pieced together so far:

The officer and Treptow were headed south on Woodcrest Drive Northwest toward 99th Avenue in Coon Rapids just before 2:30 p.m. Thursday.

Treptow, his wife, Rebecca, and their two children, ages 6 months and 6 years, were in a Buick

Rendezvous SUV. The officer drove an unmarked police car. The original dispute began at a stop sign.

Snell said investigators weren't sure what started the dispute but that it was something petty.

Both vehicles turned east on 99th Avenue. The altercation continued, with yelling and shouting. As both cars approached Foley Boulevard, the officer pulled onto the shoulder. The Rendezvous pulled up slightly behind the officer's car on the driver's side.

Meanwhile, the yelling match continued. Treptow reached past his wife in the passenger seat and fired more than one shot into the police officer's vehicle, Snell said. Despite the Treptow family's comments, investigators are not clear on whether the police officer pulled his gun. He did not fire his weapon, Snell said.

The officer got out of his vehicle and fell to the shoulder of the road. His car rolled backward across 99th Avenue and came to rest behind a pizza restaurant. The officer was treated at Hennepin County Medical Center in Minneapolis and released.

Treptow and his wife drove to a Holiday gas station across U.S. 10 and called police. Both adult Treptows were taken into custody without incident. Rebecca Treptow later was released. Martin Treptow is being held in the Anoka County Jail on suspicion of aggravated assault. His handgun was collected as evidence.

"It does not appear they knew that he was an officer," Snell said.

They didn't, Martin Treptow's family said. They say the officer never identified himself as a law enforcement official.

Treptow has a license to carry and conceal a gun, Snell said, and according to family he worked as a security guard for six years. He has no known criminal history in Minnesota, beyond a single traffic incident more than a decade ago, according to police and court records.

"We've got a renegade cop from Robbinsdale, and I'm pissed," said Martin J. Treptow, the suspect's father. "We want answers. We're getting runaround treatment."

The older Treptow said that, according to his daughter-in-law Rebecca, the officer was tailgating them closely. His son stopped because the car in front of him was pulling into a strip mall.

At some point, the officer pulled onto the shoulder, and Treptow honked, his father said. The officer stopped his car, "pulls a gun out and pointed it in my daughter-in-law's face," the suspect's father said.

"What was my son supposed to do?" Treptow asked. "People have a right to protect themselves and their family."

Nearby residents and drivers heard the shots and yelling.

Cory Alsaker and his roommate were in their apartment when they heard a gunshot. They went to the window and saw a man lying on the shoulder, both legs bleeding.

"It looked like he was shot across both kneecaps," Alsaker said.

Before placing him in the ambulance, paramedics went through the officer's pockets and pulled out a pair of handcuffs. Alsaker realized then the injured man was a police officer.

Robbinsdale Police Chief Wayne Shellum said outside the hospital that his officer was doing well, the Associated Press reported.

"He's in good spirits, and he looked at me and said, 'Geez,' he says, 'I'm sorry, Chief.' And I went, 'Hey, it's not your fault, you're doing your job, you're doing what you're paid to do.' "

Snell said the investigation continues. He said the Robbinsdale officer was on duty at the time of the shooting, but investigators don't know if he was in Coon Rapids working on a case.

Snell said the entire episode likely could have been avoided if cooler heads had prevailed.

"It wasn't just the danger for the people involved, but for everyone," he said. "There were people everywhere."

Staff reporter John Brewer contributed to this story.