One week after New Bedford police officers shot and killed a 15-year-old suspect who had allegedly attacked an officer, a preliminary investigation by the Bristol district attorney has found police tried to “de-escalate the use of force” before opening fire on the teenager.

District Attorney C. Samuel Sutter said in a prepared statement that he has determined that even after a New Bedford police detective had allegedly been stabbed by Malcolm Gracia on May 17, officers tried to avoid shooting the teenager.

Gracia was shot by police at the Temple Landing housing development after he allegedly stabbed a veteran detective working in the gang unit.

Sutter said at a news conference the next day that officers saw two males at the basketball courts at the development and attempted to talk to them when one of the males stabbed Officer Tyson Barnes. Barnes was treated and released from Rhode Island Hospital.

Sutter said Friday that police detectives used verbal commands, as well as a nonlethal taser, in an attempt to end the confrontation before firing on Gracia.

Sutter previously said other officers came to Barnes’s aid and ordered Gracia to get on the ground. While still armed, Gracia began moving toward the other officers, according to Sutter. Officers shot him and knocked him to the ground. He got up and advanced toward the officers again and they shot him again, the district attorney said.

A spokesman for Sutter said Friday night that the district attorney would not comment beyond the statement he released until the full investigation is completed.

Calls to New Bedford police and Barnes were not immediately returned Friday. Gracia’s family could not be reached for comment.

New Bedford Police Chief David A. Provencher previously said he believed his officers acted appropriately.

However, the Globe reported that about a dozen witnesses gave an account of the incident, saying they saw at least two officers with guns drawn chasing the teen up a sidewalk. The witnesses said the officers fired at Gracia as the teen was running and that he then collapsed on the sidewalk.

“I saw two officers running with their arms out holding their guns and running after him,” said Cameron Walker, 18, who said he was playing basketball with Gracia shortly before the shooting. “They were immediately on his pursuit. And then they started firing. Malcolm just collapsed.”

The statement from the district attorney on Friday said that “reports of police chasing [Gracia] are erroneous” and that a single police officer was involved in a foot pursuit of one of Gracia’s acquaintances.

The district attorney’s office also released an audio file Friday containing some police communications from the night of the incident.

“Need a medic on Cedar Street,” an officer said. “We’ve got an officer down, been stabbed.”

Other exchanges on the audio alluded to individuals on the scene that night.

“I’ve got another male, white male, black hair, sweatshirt, running north.”

“Control, I have one male take off running west on Mill.”

Sutter had previously said that his evaluation of the shooting could take up to three months.

Gracia was shot nearly three years after his father, Joseph M. Ramos Jr., was fatally shot in a confrontation with police.