Prosecutors said Fierro had reason to fear that the suspect, Richard Rodriguez, was positioning himself to attack or attempt to escape when he turned his head to face the officer while lying on the ground with his arms outstretched.

Under such circumstances, they said, El Monte officers are trained to deliver a “distraction blow” – in this case, a kick to the head – to give them time to apply some form of physical restraint.

Prosecutors said Singleterry struck Rodriguez' right arm four times with the flashlight because the suspect was refusing to pull his hand out from under his body, so the officers could cuff him.

Use-of-force experts have criticized the officers' actions as unprovoked and unnecessary.

Samuel Walker, a criminology professor at the University of Nebraska, called Fierro's reasoning for kicking Rodriguez in the head “a ridiculous rationalization.” He said the decision not to prosecute was “wrong in and of itself, and it also just confirms the belief among many in the community that officers are not going to be disciplined for excessive use of force.”

The incident began May 13 when gang officers spotted Rodriguez driving a 1992 Toyota Corolla with two passengers who gave them “nervous” looks, prosecutors said.

According to an investigation by the Los Angeles County Sheriff's Department, the officers were trying to determine if the car was stolen when Fierro noticed a 10-inch necklace hanging from the Corolla's rear-view mirror, potentially obstructing the driver's view, which is a traffic violation.

Fierro tried to pull over the Corolla by using his siren and emergency lights. But the vehicle took off, blowing through stop signs and red lights at speeds of up 100 mph, prosecutors said. When the Corolla crashed into a Lincoln in the 9400 block of Whittier Boulevard, Rodriguez sprinted away on foot.

Prosecutors noted that Fierro was alone when he first cornered Rodriguez in the walled backyard of a condominium and that the suspect hesitated before obeying Fierro's instructions to “get on the ground.”

The video footage showed Rodriguez turning to face Fierro as the officer approached him with his weapon drawn.

After Singleterry arrived and helped cuff Rodriguez, Fierro was seen in the news footage exchanging a high-five with another officer.

“All of the interviewed officers stated that such gestures are commonplace after pursuits to signify relief that no one was injured and that the suspect was captured,” the evaluation said.

Medical records show that Rodriguez suffered “superficial abrasions” to the face and did not complain of pain after the arrest, which prosecutors argued was more consistent with a blow intended to stun than one done out of anger or vindictiveness.