The Orange County district attorney's office has declared that four members of the Fountain Valley Police Department are not criminally culpable for the nonfatal shooting of a 17-year-old boy in 2010.

A May 15 letter from Senior Deputy District Attorney Aleta Bryant, which the office released Friday, concludes that Officer Richard Nilos, Det. Kham Vang, Det. Pat Estes and Sgt. Kurt Ulrich acted legally and reasonably when they shot David Dinh in an apartment complex courtyard.

The office reached its findings after interviewing 69 witnesses and examining incident reports and other evidence, the letter states.

Spokeswoman Farrah Emami said her office's Special Assignment Unit automatically investigates any officer-involved shooting in which a person is injured or killed, regardless of whether anyone questions the officers' actions.

"Whether there is any type of attention or not, it's our responsibility to review officer-involved shootings to determine if there's any criminal culpability on the part of the officers," she said.

The 25-page letter, which includes accounts of the incident by Dinh, the officers and witnesses, concludes that each of the officers "was in actual fear for his own life" and that their actions were "reasonable and justified" given the circumstances.

Dinh's defense attorney, Lewis Rosenblum, did not return calls seeking comment.

On Dec. 28, 2010, a resident called police and said an intruder, later identified as Dinh, had stormed into his apartment, ordered him to the floor with a gun and threatened to kill him. The resident escaped, and with officers outside, Dinh armed himself with a rifle owned by the resident, walked out of the apartment and exchanged fire with the officers.

He suffered wounds to his arms, legs and upper torso and was handcuffed and taken into custody.

Dinh was convicted July 15 of attempted voluntary manslaughter and assault with a semiautomatic firearm, with a sentencing enhancement for the personal use of a firearm and felony false imprisonment by force or violence. He was sentenced to 10 years and two months in state prison.

michael.miller@latimes.com

Twitter: @MichaelMillerHB