Zarate had gunshot residue on his hands — one tiny particle

Forensic evidence doesn't seem to add much to the prosecution's case

An expert in forensic science testified Friday that Jose Ines Garcia Zarate has exactly one particle of gunshot residue on his hands – enough for the prosecution to claim as evidence that he fired a pistol, but little enough to give the defense grounds to argue that it was inconclusive.

Linda Abuan, who works at the San Francisco crime lab, explained to the jury that every time a firearm is discharged, it releases hundreds of microscopic particles, some only 1/40th the thickness of a human hair.

When a gun fires, thousands of tiny particles escape. Wikipedia image

A distinctive particle, which contains antimony, barium, and lead, is characteristic of that residue, she said. And the discovery of any amount on a person’s hands indicates that the person “fired a gun, was close when a gun was fired, or touched something with GSR on it.”

She went through the testing procedure, which involves a scanning electron microscope searching swabs taken from a suspect’s hands. In this case, the microscope found one particle that didn’t appear to have the characteristics of GSR.

But, following standard procedures, Abuan went back and manually examined that particle and decided that it fit the profile.

It’s not a quantitative test, she said: “We are just looking to see if it is present or not.” So one microscopic particle can trigger a positive result.

On cross-examination, Matt Gonzalez, representing Zarate, asked her if everyone in the forensic world agreed that the presence of one particle was enough to demonstrate that the person had fired a weapon. In Baltimore, he said, the Police Department considers five particles the minimum for a positive identification. Abuan acknowledged that there is no commonly accepted threshold.

In fact, Gonzalez pointed out, researches in Los Angeles found GSR in 45 of 50 samples from the back seat of police cars. The FBI lab in Quantico has found it on desks and railings.

Abuan said that GSR can be spread easily by contact; she compared it to talcum powder. It can last for weeks or months, she said; it doesn’t degrade and remains where it was until is it brushed or washed away.

Judge Samuel Feng has been very strict about limiting questions in corss-examination, the courts don’t like speculation. We are under no such rules, so we can raise the question:

If, as the defense argues, Zarate was holding the gun, possibly wrapped in a shirt, when it discharged, then tossed it, possibly still wrapped in cloth, into the Bay, he might have had only a limited amount of GSR on his hand.

On the other hand, some people fire a weapon and get almost no GSR.

I’m not sure how much that testimony proved, particularly since the defense isn’t denying that Zarate was close to the weapon when it fired.


  1. I said nothing about perjury. You know as well as I do that had their been a lot of power residue, the DA would be waving it in Gonzalez’s face, and shouting that it proved that Zarate had murdered Steinle. She is just spinning things to fit her agenda, which has nothing to do with the truth. I am simply pointing out that the DA is trying to explain away inconvenient facts, in a way that many of the haters and bigots are also doing. I realize that “reasonable doubt” is a nightmare for you.

  2. That is pretty big. I read several accounts about the gun residue but nobody mentioned the 45 minute delay. Did anybody report on it?

  3. I am sure the prosecutor was very careful to coach the tech to make that sort of claim.

    Wow!!!! So the DA’s office instructed the police technician to commit perjury about an established departmental policy. And she did it!II This is big news!!!

  4. Naw,

    He was in the back seat of the squad car for 45 minutes before his hands were ‘bagged’. That came out too.

    I’m an old dog and it amazes me how much of this was captured on video.

    They have everything from the defendant leaving the pier all the way up to his apprehension on tape.


  5. I read the article. I am sure the prosecutor was very careful to coach the tech to make that sort of claim. The low amount, and the missing shell casing you keep trying to hand wave away, are called REASONABLE DOUBT. So far, the prosecution has really offered nothing that remotely proves he is guilty. Of course, for some, that doesn’t matter. You will believe what you want, and will continue to after he is acquitted.

  6. Here’s a thought — read the article. The SFPD regards the results as binary; either the gun residue is there or it isn’t. The best that Gonzalez could do is to point out that the city of Baltimore requires 5 particles to be conclusive. And as even Tim says “On the other hand, some people fire a weapon and get almost no GSR.”


  7. Well, let’s see…. He was taken into custody very shortly afterwards, his hands were covered with paper bags, and there is nothing to indicate that he had been able to clean his hands. In fact, he had quite a few particles from crackers that he had been eating. So, this person can try, rather desperately, to hand wave away the facts about the shell casing, and the GSR, but it was not 4-6 hours before he was arrested. It was, in fact, one hour. Whoops, again hoist by her own petard…

  8. Yes, by all appearances, they followed proper procedures. And wound up providing evidence that supports the defense. Much to the chagrin of those who want him railroaded.

  9. Sorry, paper bags. It still seems as if the police followed proper procedures or else Gonzalez would have let everyone know.

  10. Actually they wrapped his hands in paper bags. I don’t know what difference that makes, not sure when they were wrapped. Nobody says he wasn’t close to the gun when it fired.

  11. I think so…it is S.O.P in these cases. They did wrap his hands in plastic bags before they put him in the police car. Tim left that part out of an otherwise detailed article for some reason.

  12. “I’m not sure how much that testimony proved, particularly since the defense isn’t denying that Zarate was close to the weapon when it fired.”

    If I had to guess, I’d say that Gonzales is highlighting anything that might make the jury think that the police were overall careless in their investigation.

  13. A good analysis of powder residue and what it proves or doesn’t prove, including what the lack of residue proves or doesn’t prove (in short, lack of residue proves nothing at all, just like the lack of a shell casing on the pier proves nothing at all). Also, powder residue, or gun shot residue, usually only remains on hands 4-6 hours, so its presence or lack thereof is not necessarily incontrovertible evidence of anything

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