Many questions remained Sunday about what led a gunman in Fargo, North Dakota, to open fire on police officers as they were responding to a traffic crash. One officer was killed and two others were critically wounded before the gunman was killed by a fourth officer.

The shooting happened Friday afternoon along a busy street, and roughly nine hours passed before authorities told the public that officers were shot. On Saturday, Fargo’s police chief released the names of the officers and the name of the gunman, but said the motive was unclear and that the 37-year-old man opened fire for “no known reason at all.”

Chief Dave Zibolski also said little about how the situation unfolded, noting the investigation was in the hands of state and federal investigators.

“We are not in the position to provide many details in terms of the actual incident itself,” Zibolski said. Authorities released no new information Sunday.

Here’s what we know, and what we don’t, about the shooting:

WHAT HAPPENED AT THE SCENE?

Police and fire officials were responding to a “routine” traffic accident on a busy street Friday afternoon, when a gunman began firing multiple rounds at them — killing one and wounding two, Zibolski said. A fourth officer shot and killed the man, who authorities identified as Mohamad Barakat of Fargo.

Zibolski described the first few minutes as “very chaotic,” but said that firefighters on scene and a nearby ambulance were essential in preventing additional fatalities. As soon as the firing stopped, “firefighters bounced out and they were applying first aid immediately to our officers,” Zibolski said, which “probably had a very significant impact on their survival.

Authorities released few details about what happened in the moments before Barakat began firing and his motive was not clear.

“The first thing we always want to know in a situation like this is, ‘Why?’” Zibolski said. “Why would somebody do this?”

WHAT DID WITNESSES SEE?

Among the drivers who witnessed what happened was Chenoa Peterson. She told The Associated Press on Saturday that a man appeared to have ambushed the officers. The gunman was at the rear of a car in a bank parking lot near the traffic crash when he fired on an officer not more than 20 feet (6 meters) away, she said.

“He was holding up the trunk of the car with his arm, and then I see the gun come up, and he set it on his shoulder and just pointed it directly at an officer in front of him,” Peterson said. “It was like 10 shots right away.”

Officers weren’t looking in the direction of the gunman when he began shooting, she said.

Peterson’s 22-year-old daughter was with her and said the suspect exchanged simultaneous gunfire with police.

“I saw them firing at each other both at once,” Katriel Peterson said. “But soon as the shooter took a break the cop came walking towards him letting off round after round. There was already an officer down. And a family hiding just on the other side of the vehicle next to the shooter.”

WHAT DO WE KNOW ABOUT THE FALLEN OFFICER?

Officer Jake Wallin, 23, was killed. Zibolski said Saturday that his wounds were fatal and “there was nothing that could be done.”

A military veteran, Wallin previously served in the Minnesota Army National Guard and was deployed to Afghanistan, Zibolski said.

“He served his country, came back here and wanted nothing more but to serve in a position with purpose and meaning — his exact words — and he did that,” Zibolski said. Zibolski spoke to his sense of humor and his excellence throughout training, calling him a member of the department family.

In video played at a Saturday news conference showing Wallin training with fellow recruits, he spoke of his desire to pursue a career in law enforcement.

“Throughout my entire life, I’ve always wanted to work in some sort of position that had purpose behind my job and police officer is always what kind of came to me,” said Wallin of St. Michael, Minnesota,. “I don’t want to be sitting in an office wondering why I’m here every day. I want to be out, I want to be doing something that I can tell myself at the end of the day I made a difference somehow.”

Funeral arrangements have not been made public. The governor has ordered that flags be flown at half-staff on the day of Wallin’s interment.

HOW ARE THE OTHER VICTIMS?

Two other officers, Andrew Dotas and Tyler Hawes, were in critical but stable condition as of Saturday, and Zibolski said they were in “good spirits” but had significant recovery ahead of them. No update on their condition was provided Sunday.

Wallin and Hawes were both young recruits, sworn in less than three months earlier and still in training when they responded to the scene. Dotus was a six-year veteran who was responsible for training officers.

A fourth officer, Zach Robinson, shot and killed Barakat, Zibolski said.

A 25-year-old female bystander also was injured in the shooting, though authorities haven’t said who shot her. A hospital spokesman said Sunday that she was in fair condition.

WHAT HAPPENED AFTERWARD?

Shortly after the shooting, authorities, including the FBI, converged on a residential area about 2 miles (3.2 kilometers) away and evacuated residents of an apartment building to gather what they said was related evidence. Court documents that would indicate what authorities were looking for have not been made public and authorities have said little about that search, other than to say it was happening at the time.

On Saturday, investigators were still at the apartment building, going back and forth from the third floor, where police tape hung across a hallway. Few residents were around and an FBI truck was out front.

WHAT WE KNOW ABOUT THE SUSPECT

The city also has said little about Barakat or the gun he used. Zibolski said he believed police previously had some sort of contact with Barakat “but not anything significant.”

Zibolski said it does not appear that Barakat was involved in the car crash that brought officers to the scene but indicated investigators are determining whether this was a planned ambush of officers.

Zibolski said he was confident authorities would eventually understand Barakat’s motive and that information would be made public at the appropriate time.