REDWOOD CITY -- An investigation into the June officer-involved shooting death of a teenage girl in Half Moon Bay has led the District Attorney to find the deputy's actions were justified in defense of his own life.

Deputy Menh Trieu, a nine-year veteran of the San Mateo County Sheriff's Office, will not face any criminal charges for the June 3 killing of Yanira Serrano-Garcia, a mentally-ill 18-year-old whom he shot once in the upper torso as she advanced at him with a 10½-inch kitchen knife, District Attorney Steve Wagstaffe said.

The deputy's actions were in line with standards set forth for officer safety, the DA said, and may have saved his own life.

"He only had time to make one choice," Wagstaffe said in an interview Monday. "And it's clear that the deputy sheriff did not want to shoot this woman."

Serrano-Garcia's family and their attorneys could not be reached for comment.

Trieu, who officials said had not undergone CIT training, a 40-hour state-certified curriculum focusing on mental illness, shot and killed Serrano-Garcia at 9:23 p.m. down the street from her home in the Moonridge Housing Complex. Her brother, Tony Serrano-Garcia, called police to report she refused to take her medication and was "acting out" on her parents.

When he told dispatchers she had a knife, the unarmed responders adhered to county protocol, waiting at the end of the street as Trieu responded first.


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Trieu parked his car on nearby Chamomile Drive when his GPS was unable to locate the exact residence. The Serrano-Garcia residence is located facing a sidewalk, and it does not register as a street on GPS, Wagstaffe said.

Trieu found the teen's residence on foot, and Serrano-Garcia saw him coming through a window of the house, Wagstaffe said. The teen reportedly lashed out in anger at her family for calling 911, an action that previously landed her in the hospital.

As Trieu stood on the sidewalk unsuccessfully trying to communicate with the teen's Spanish-speaking mother, Serrano-Garcia ran off the front porch with the knife raised over her head, screaming in Spanish, "You're not going to take me!" in a tone witnesses described as "primal, incoherent and garbled."

Wagstaffe said Trieu began retreating backward when she ignored multiple commands to stop, running 157 feet back to his patrol car. He ran past his vehicle hoping his partner had arrived and realized he was alone without backup.

Trieu pulled his gun as the young woman began to close the distance between them, moving "incredibly quickly" despite being obese and having a birth defect that caused her to walk with a limp, Wagstaffe said. Trieu again ordered her to stop and put the knife down, but she kept running.

Trieu fired one shot into the upper center of her chest from eight to 10 feet away, then kicked the knife away with the sole of his boot as she fell to the ground. He checked on the teen, then stepped to the street, waving his flashlight up and down to signal the waiting fire crews and medics.

According to the DA, the other deputy also couldn't find the residence.

Trieu told investigators the next day that he wouldn't have been able to unsnap and unbuckle his Taser quickly enough to deploy it and that he questioned whether the prongs would have made contact with her body through the bulky sweater she was wearing. He maintained that he did not think there was any way he could have used less lethal force.

"There is not one component of this case that isn't sad," Wagstaffe remarked. "Whatever was going on inside Ms. Seranno-Garcia's mind, there was no magic that could have been worked to make her stop."

The incident marked the second officer-involved shooting in San Mateo County this year, making 2014 the first year since 2006 with more than one officer-involved shooting. Of the six fatal officer-involved shootings since 2010, four involved patients who were mentally ill, authorities said.

Trieu has returned to work and is assigned to the San Mateo County jail, San Mateo County Sheriff Greg Munks said.

Munks added that his office plans to host a community meeting in coming weeks to discuss the outcome of the investigation, as well as introduce a new pilot program with a goal of coordinating efforts between the sheriff's office and county behavioral health department.

Serrano-Garcia's death prompted the development of an on-call team of mental health professionals to assist deputies in their interactions with mentally-ill individuals.

Jonathan Melrod and Armando Casillas, attorneys for the Serrano-Garcia family, maintained that the authorities, including Trieu, "had to have known (the young woman)" and been familiar with her issues when they responded to the home that day, since the sheriff's substation is mere yards from the family home. According to Wagstaffe, both deputies involved said they had never had any prior contact with Serrano-Garcia.

Follow Erin Ivie at Twitter.com/erin_ivie.