Jacai Colson, 28, who had four years’ service on the Prince George’s County police force, was killed March 13, 2016. (Reuters)

When Prince George’s County police officer Taylor Krauss fired the shots that ultimately killed a colleague, according to prosecutors, he did not think he was taking down an officer but rather protecting one.

New details emerged Friday about the chaotic scene that left undercover detective Jacai Colson dead after an attack on a police station in March; prosecutors announced that a grand jury had declined to indict Krauss in Colson’s death.

Colson, 28, was one of several officers who arrived at a county police station in Landover, Md., on March 13 after officers inside reported that someone was shooting into the building, authorities said. Prosecutors say three brothers planned the attack on the station, with the goal of gaining notoriety by recording a video of the assault and posting it on the Internet.

Amid the gunfire exchanged by police and one suspect, Krauss shot Colson, who was off-duty and in street clothes.

The shots that mortally wounded Colson were fired in the moments after a uniformed officer in a marked cruiser pulled up to the scene and opened his car door, Prince George’s County State’s Attorney Angela Alsobrooks said Friday.

Colson was down the street firing toward where suspects were and where officers were advancing, prosecutors said. Krauss saw what he thought was another civilian with a gun firing toward the police station, Alsobrooks said in explaining the events.

Krauss “believes he is protecting the officer who comes up” in the marked car and who would be unaware of what Krauss had taken to be an additional threatening shooter, Alsobrooks said.

The grand jury rendered its decision a few weeks ago, but prosecutors delayed announcing the results until after they could meet with Colson’s family to review the findings, Alsobrooks said.

Reached by phone Friday, Colson’s mother, Sheila Colson, would say only that she, Jacai’s father, James Colson, and brother Jurea Colson, were “highly disappointed” with the grand jury’s findings.

The grand jury met for seven weeks to sift through dozens of witness statements, videos, forensic evidence and other material to decide whether Krauss should face charges, including first-degree murder, manslaughter and misconduct in office, Alsobrooks said. The grand jury also visited the scene of the shooting.

One of the key legal elements the grand jury had to consider was “not merely whether the actions were negligent, but whether or not the actions of this officer in the mind of a reasonable person acting in his position would have been reckless,” Alsobrooks said.

The shooting unfolded quickly, and Colson’s work as an undercover officer is likely to have played into the grand jury’s decision, Alsobrooks said.

The killing of Colson — who was black — occurred as the country grapples with continuing concerns about race-based policing and implicit bias. Alsobrooks said the grand jury also tackled such issues in considering charges against Krauss, who is white.

“Those were all things that the grand jury had a full opportunity to discuss and ask questions about,” Alsobrooks said. “We also explored all of that with them and what the relationships were between all the officers.”

Now that prosecutors have completed their investigation, the police department will begin an administrative review of the case, said Lt. Dave Coleman, a county police spokesman. Krauss, who has six years of service with the department, was a patrol officer assigned to the station where the shooting occurred. He has been on administrative leave and will remain in that status until the internal review has been completed.

Alsobrooks said her office will move forward with the case against three brothers who were arrested in connection with the shooting at the police station that brought Colson, Krauss and other officers to the scene.

Michael Ford, 23, Malik Ford, 21, and Elijah Ford, 18, have been charged with murder and related charges in Colson’s death. Prosecutors say Michael Ford carried out the attack on police while the other two watched and recorded it.

A trial date for the Ford brothers has been tentatively set for October.