FILE - In this Aug. 18, 2015, file photo, former Albuquerque Detective Keith Sandy, left, and Officer Dominique Perez speak with attorneys during a preliminary hearing in Albuquerque, N.M. Perez took the stand Tuesday, Oct. 4, 2016, to testify in his own defense, marking the first time either officer has spoken publicly about the 2014 shooting that killed 38-year-old James Boyd and derailed the officers' law enforcement careers. (AP Photo/Russell Contreras, File)

ALBUQUERQUE, N.M. - A homeless camper with knives in his pockets pulled out the blades and took an "aggressive fighting stance" in the seconds before two Albuquerque police officers fatally shot the man, one of the officers testified Tuesday.

Ex-Officer Dominique Perez's testimony during the third week of the jury trial for him and now-retired Detective Keith Sandy marked the first time either officer has spoken publicly since the 2014 shooting that ended an hourslong standoff with nearly 20 officers and led to unrest in New Mexico's largest city. Both are charged with second-degree murder in the death of James Boyd, who suffered from schizophrenia and was camping illegally in the Sandia Mountain foothills.

Perez, 35, calmly answered questions from his attorney Luis Robles and special prosecutor Randi McGinn about how he shot an armed and erratic Boyd in the back with his rifle.

He said he opened fire as a K-9 handler and police dog advanced on the camper — a statement in line with defence attorneys' argument that the officers were obligated to shoot to protect the K-9 handler.

"At this point I'm extremely focused," Perez said. "My perception is he is within an arm's reach."

A crime scene analysis later deterimined that the K-9 handler was more than 9 feet from Boyd.

Perez's testimony resumes Wednesday. Sandy, who has been targeted more so than Perez for his alleged role in escalating the standoff, also is expected to testify in his defence before the case is sent to jurors.

"I can't tell you how sorry I am that you are the one who was sent into a mess that some other officer created," McGinn, the prosecutor, told Perez before quizzing him on how he placed Boyd in the scope of his rifle and fired the weapon with .223-calibre bullets.

McGinn suggested during questioning that the bullets can cause more damage to the human body than other types of ammunition.

Prosecutors' arguments and testimony from dozens of officers has renewed scrutiny of Albuquerque police's paramilitary response to the 2014 standoff and shortfalls at the time in other encounters with the mentally ill. The trial also has unfolded as shootings in other states have led to outcry over race and how law enforcement officers respond to calls involving people with mental illness.

In Albuquerque, the shooting — captured on video by Perez's helmet camera — spurred calls from the city's mayor for the U.S. Justice Department to speed an investigation into accusations of excessive force by local officers.

That investigation later found a "culture of aggression" within the Albuquerque Police Department and set the stage for a settlement agreement to overhaul how officers deal with the mentally ill and people in crisis.

With Boyd, the encounter began when a resident reported his illegal campsite situated several hundred feet behind some homes. The two officers who responded with weapons draw but not pointed at Boyd called for help after they tried to pat him down and the camper pulled knives out of his pockets.

Nearly 20 officers responded to the scene with rifles, handguns, hundreds of rounds of ammunition, and a Taser shotgun.

Perez was among the last to arrive after his SWAT sergeant asked him to respond. He testified that he joined officers from another unit on the hillside below Boyd's campsite knowing that they had a plan to take Boyd into custody with less-lethal force but not knowing what that plan was.

Sandy detonated a smoke bomb to the right of Boyd, who was gathering his belongings and telling officers he would walk down the hillside with them. The bang was meant to startle Boyd, but it instead appeared to prompt him to pull two knives as the K-9 unit advanced on him and officers ordered him to get on the ground.

Sandy fired first, then Perez.

Perez testified that his bullet struck Boyd in the back because he began pulling the trigger in the same split-second the camper started turning away from police.

"All the things that occurred that day happened in the blink of an eye — happened at the speed of light," Perez said.

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Follow Mary Hudetz on Twitter at http://twitter.com/marymhudetz. Her work can be found at http://bigstory.ap.org/journalist/mary-hudetz.

News from © The Associated Press, 2016