An independent review backs a D.C. police finding that an officer’s fatal shooting of a young man in September was justified but says mistakes made by police before the deadly encounter unnecessarily put officers and the suspect in danger.

The report into the Sept. 2 shooting of 18-year-old Deon Kay in Southeast Washington also found supervision of the department’s Crime Suppression Team, which was involved in the encounter, to be lacking, and it questions the thoroughness of the police investigation.

The review, commissioned by the District’s auditor, Kathleen Patterson, is the latest effort by her office to scrutinize deadly encounters involving police and how the department investigates them. An audit completed in March of other incidents reached similar conclusions.

The audit made public Tuesday found Officer Alexander Alvarez had a split second to react upon confronting Kay as the young man ran toward the officer and raised his right hand while holding a gun. The two were about eight feet apart, the report says, and Kay threw the gun away about the same time the officer fired.

Although Alvarez — among a group of officers that tracked down Kay and others after seeing them with firearms on Instagram Live — had been justified in firing, “effective policing in the moments leading up to that split second may well have prevented that split second from arriving,” Patterson wrote in a letter to city officials.

The audit, which recommends new training and protocols, criticizes the officers for failing to develop a tactical plan to arrest the occupants of the vehicle, and for not keeping their supervisors informed about their plans that night. The report was written by the Bromwich Group, a consulting firm that also conducted the previous review of deaths involving D.C. police.

D.C. Police Chief Robert J. Contee III wrote to Patterson saying that he agreed with most of the audit’s conclusions and promising to “remain open to examining and improving our policies and training to ensure that deadly force is used only as a last resort.”

Contee said the department would develop new policies on how and when officers could chase someone on foot and on the use of social media during investigations. He also said he would more clearly define the scope and duties of Crime Suppression Teams, of which Alvarez was a part. The chief previously promised to ensure more-thorough reviews of fatalities involving police.

Yaida O. Ford, a Kay family attorney, called the audit report inconsistent, saying reviewers should not have agreed that the shooting was justified if they also thought it might have been avoided with better tactics or preparation.

She said police “created a dangerous situation that could have been avoided.”

Efforts to reach Alvarez, who has since returned to duty, were not successful. The police union did not respond to a request for comment.

Some police experts had praised Alvarez and the other officers for acting quickly to confront suspected gunmen to avert possible violence, while others, such as members of the District’s Police Reform Commission, wondered whether a different approach could have been used to target illegal firearms in a less dangerous way.

During a public meeting a week after Kay was killed, commission member Patrice Sulton, director of the DC Justice Lab, told then-Police Chief Peter Newsham that his public statements “emphasized why the shooting was justified, and not whether it was avoidable. ... You’ve been focusing on whether it was necessary in the moment instead of whether it was necessary at all.”

Kay was shot after members of the 7th Police District Crime Suppression Team watching a live stream on Instagram saw four young men brandishing two firearms in a parked vehicle. The officers were able to identify the general area where they thought the Dodge Caliber was parked and later found it backed into a space at an apartment complex in Congress Heights.

As officers pulled up in an unmarked vehicle, one man jumped from the Caliber and ran. Alvarez started after him, passing the Caliber, according to the audit report, but quickly gave up when the man pulled far ahead.

Alvarez turned back toward the Caliber as Kay jumped out and ran toward him, raising his right arm while holding a gun. Alvarez’s body camera video shows him firing it at around the same moment as Kay threw the weapon down an embankment. Kay was struck in the chest.

Federal prosecutors said in November that they would not file charges against Alvarez, saying they could not determine beyond a reasonable doubt that the officer committed “willful violations” of federal criminal civil rights statutes.

The audit made public Tuesday for the first time reveals that the D.C. police Internal Affairs Bureau later found the shooting to be justified and within department policy.

The department’s Use of Force Review Board, made up of police officials who review internal investigations of cases involving serious injury or death, agreed with internal affairs but also said tactical errors were made, according to the audit.

The review board’s decisions are not public. According to the audit, the board concluded that “the tactics used by Officer Alvarez and his colleagues were deeply flawed and unnecessarily created a threat to both the officers and the suspects.”

The audit says that after the officers saw the live stream of Kay, “they immediately launched a search ... without consulting a higher level of management,” and when “events unfolded rapidly and unpredictably,” they “squandered any opportunity to de-escalate the situation and limit that risk.”

Auditors specifically criticized Alvarez for running past the Dodge during his initial, aborted pursuit, putting himself in front of a vehicle he knew was occupied by armed people.

Ford, the Kay family attorney, said Deon Kay was trying to run away and inadvertently crossed paths with Alvarez after the officer tried to chase the first man. “Deon was already in the process of throwing the weapon” when Alvarez fired, she said. “Deon was not looking for trouble that day,” she said. “He was not looking to shoot a cop. He was trying to get the hell out of dodge.”

The auditors also criticized supervision of the Crime Suppression Team. The report says a lieutenant “was not generally well informed” about the squad’s activities. It also says a sergeant “did not formulate a specific plan in advance of finding the Dodge in the parking lot, and had no plan for what to do if they found the suspects they had been searching for.”