Bullet Trajectory and Ricochet Shot Central to Steinle Murder Trial

A retired San Francisco crime scene investigator testified Monday in the high-profile murder trial over the 2015 slaying of Kathryn Steinle that "firearms do not fire by themselves."

It's a simple point that's at the heart of whether defendant Jose Ines Garcia Zarate will be found guilty of murdering 32-year-old Steinle, whom he had never met, as she walked with her father on San Francisco's waterfront.

To justify a murder conviction, the prosecution must prove Garcia Zarate intended to fire the gun at Steinle or a crowd of people gathered on Pier 14 about an hour before sunset on July 1, 2015. The defense is arguing Steinle's death was an accident: that Garcia Zarate picked up an unknown object wrapped in cloth from beneath a rotating metal chair on the pier. The gun was stolen from a U.S. Bureau of Land Management ranger four days before the the killing, and the defense argues it accidentally fired as Garcia Zarate unwrapped it.

Assistant District Attorney Diana Garcia called since-retired SFPD officer and crime scene investigator John Evans to testify on Monday. He said the initial investigation of the pier on July 1, 2015, turned up no evidence.

But after a bullet that had been flattened on one side was extracted from Steinle's body, Evans and his team of crime scene investigators returned to the pier, determined through an "exhaustive search" to find the place where the bullet struck before it hit Steinle in the back.

And on July 5, 2015, investigators found a chip in the concrete 12 to 15 feet from where Garcia Zarate was believed to be sitting and about 78 feet from where Steinle fell to the ground.

But that one point alone was not enough to reconstruct the trajectory of the bullet, Evans testified. He would need two "known, fixed points" that the bullet hit in order to determine the bullet's path.

Instead, Evans conducted what he called a "vector analysis" to see if it was at least possible for the shot to have originated from approximately where Garcia Zarate was sitting, ricochet off the concrete and hit Steinle.

They did it by pointing a laser from one of a pair of metal chairs. (It was unclear which one Garcia Zarate was in at the time of their investigation, Evans testified.) He found an unobstructed, straight line from the chair to the divot in the concrete, and another line from there to approximately where Steinle was standing.

Prosecutor Diana Garcia asked Evans whether he'd formed an overall opinion about the shooting, and he was allowed to answer over objections from Garcia Zarate's defense attorney.

"A human being held a firearm, pointed it in the direction of Ms. Steinle, pulled the trigger and fired, killing her,” Evans testified. "That is the only way this could have occurred, that is reasonable."

On the ricochet, Evans described an action he called "jerking the trigger," in which a person -- generally an inexperienced shooter, pulls the trigger harder than necessary, causing the barrel to dip. He said that can result in what he called a "skip shot."

"It can be intentional or unintentional, but it's where the bullet that is fired strikes a hard surface in the direction of the target but short of the target," he said.

Defense attorney Matt Gonzalez tried to deconstruct Evans' conclusion during cross examination.

"A trajectory analysis was not conducted because we don't have the basic elements of a trajectory analysis," Gonzalez said in court. "I've been doing this for 25 years and I've never seen a witness talk about a subset of trajectory analysis called vector analysis. I'm surprised."

Gonzalez went through a long line of questioning about whether a ricochet would change the direction that a bullet was traveling. Evans said it did, vertically, but from the top, down or from the perspective of the shooter, it would still appear to be a straight line.

"I didn’t find it convincing," Gonzalez said outside of court. He said the defense plans to call expert witnesses on bullet trajectory. "They’re going to tell you that bullet hit the concrete, and it’s not traveling straight anymore. It’s moving to the side, it’s moving vertically, and every time you do that, you’re going to have a different result. That’s the whole point."