The police in Albuquerque said they were investigating whether their tactics during a standoff last week contributed to a house fire in which a teenager died, and called for patience from protesters who believe he was shot.
The police on Sunday identified the teenager, Brett Rosenau, 15, and said the preliminary results of an autopsy determined that the cause of death was smoke inhalation.
In a statement, the department said he “was not shot by anyone” during the standoff, in which officers arrested a man they had been seeking, Qiaunt Kelley, 27, on a warrant for a parole violation.
“I know many people in our community are hurting right now, and appreciate everyone’s patience while the incident is thoroughly investigated,” Chief Harold Medina said in the statement. “If any of our actions inadvertently contributed to his death, we will take steps to ensure this never happens again.”
Mr. Rosenau’s family said in a statement that they supported a request by the American Civil Liberties Union of New Mexico to have the state’s attorney general, Hector Balderas, investigate the death.
In the statement, the family described Mr. Rosenau as a smart and funny teenager who liked football and baseball and taking apart and rebuilding bicycles, and who was “always interested in creating something new.”
“The police conduct on July 6, 2022, can only be described as tragic and completely avoidable,” said the statement released by the family’s lawyers, Carey Bhalla and Taylor E. Smith. “The police had every opportunity to save Brett’s life but instead chose inaction. Brett’s family and community are forever left without their son, brother and friend.”
In a statement, Mr. Balderas said, “I am troubled by the recent loss of life of the young teenager in our community, and my office will offer assistance to ensure that appropriate actions were taken during this law enforcement operation.”
Elizabeth Fields, whose sister Sundra Coleman owned the house, said she witnessed the standoff from Wednesday night to Thursday morning. She said that the police threw smoke grenades and flash bangs into the house every 30 minutes for five and a half hours and then let the house burn for 40 minutes after it caught fire at around 2:30 a.m. on Thursday.
“They treated and trapped them like animals,” Ms. Fields said in an interview on Tuesday. “There was no way these Black men were going to come out.”
She said the fire left her sister’s family homeless.
“The whole house is completely burnt out,” she said. “All of our family pictures — everything gone — and the family dog died inside.”
The episode brought renewed scrutiny of the department’s track record. That record was the subject of a 2014 agreement with the U.S. Department of Justice to introduce reforms and oversee the police’s use-of-force tactics, accountability, training and community engagement.
The agreement was reached after the Justice Department found a pattern of excessive force by the police: Twenty-three people were killed and 14 were wounded in police shootings over four years.
Under the agreement, the police are required to report to the Justice Department details of the investigation into Mr. Rosenau’s death, the police said. They will also release video footage from officers or drones that was taken during the standoff, the department said.
The release of the statement on Sunday was at least the second time in two days that the chief had tried to defend his department and appeal for calm. On Thursday night, dozens of people gathered to protest the death of the teenager, who was Black, The Albuquerque Journal reported.
In a news conference last week, Chief Medina urged the public to wait “before a determination is made that impacts the quality of our city.”
He said that a launcher used to deploy tear gas and powder canisters into the house might have led bystanders to believe there was gunfire. “We have no indication that any shots were fired by the Albuquerque Police Department,” the chief said.
The episode unfolded late on Wednesday as detectives searched for Mr. Kelley. Mr. Kelley had violated the terms of his probation for armed carjacking and stolen vehicle charges and was also being sought in connection with a fatal shooting, a recent armed robbery and another shooting in which someone fired an automatic weapon at officers, the department said.
The police tracked him to a house in southeast Albuquerque, the most populous city in New Mexico with a population of more than half a million. They saw a gun in the car he was in and determined the motorcycle he was working on at the residence was stolen, the police statement said.
Mr. Kelley barricaded himself inside the house. Mr. Rosenau, whom the police were not seeking, followed Mr. Kelley into the house, the police said. Law enforcement officers “tried for several hours to convince them to peacefully” exit, the statement said.
Officers used a drone and robots to determine who was inside. Sgt. Michael Jones, a tactical officer, said during the news conference last week that officers deployed a Tri-Chamber Flameless Grenade device, commonly used in crowd control, that disperses tear gas and powder to make the environment “uncomfortable.”
The standoff ended after officers noticed smoke coming from the house, the department said. As firefighters arrived, Mr. Kelley emerged and was arrested, then was treated at a hospital for burns. Mr. Rosenau was found dead inside the house, the police said.
Albuquerque Fire Rescue is investigating the cause of the fire, which will probably take about two weeks, the police said.
Defense Technology, which makes the Tri-Chamber Flameless Grenade device, says on its website it “provides the option of delivering a pyrotechnic chemical device indoors, maximizing the chemicals’ effectiveness via heat and vaporization while minimizing or negating the chance of fire to the structure.”
The police statement said that Chief Medina acknowledged the possibility that the “devices used to introduce irritants into the home may have caused the fire.” It added that “no fires have been reported over the many years they have been used in Albuquerque.”
The A.C.L.U. of New Mexico said in a statement that the facts “present real questions concerning the training and experience of A.P.D.’s SWAT team and the dangers presented if tear gas canisters are used improperly.”
Barron Jones, senior policy strategist at the A.C.L.U. of New Mexico, said in the statement, “Rosenau’s loved ones deserve answers and our community must be assured that proper accountability will be applied to fatal police encounters like this one.”
Michael Levenson contributed reporting. Susan C. Beachy contributed research.