Trayvon Martin: What Forensics Can Tell Us


We already know that two independent forensic audiologists have examined a recording of a 911 call by a woman who reported a struggle going on behind her residence. A long high-pitched scream for help that is audible in the background terminates abruptly with what sounds like a single shot.

Using different analytical methods the two experts have compared the scream to a police recording of George Zimmerman’s voice when he called a police non-emergency number approximately 10 to 15 minutes before the shooting to report a suspicious person in his neighborhood.

We now know that person was Trayvon Martin, who was walking back to his father’s girlfriend’s residence, whom he was visiting with his father, after walking to a nearby 711 store to purchase some Skittles and Arizona Iced Tea.

Both experts excluded George Zimmerman as the person screaming in the background to a reasonable scientific certainty. They have not compared the scream to a recording of Trayvon Martin’s voice, presumably because they do not have a recording of his voice.

Trayvon Martin’s mother has identified her son as the person screaming.

Since there is a witness who claims to have seen the struggle between Zimmerman and Martin with Martin on top and Zimmerman lying on his back in the grass yelling for help, there is an apparent conflict in the evidence between the eyewitness’s statement and the two expert opinions. I say “apparent conflict” because the witness did not observe the fatal shot. He locked his door, went upstairs, and when he looked out the window, he saw Martin lying face down in the grass and not moving.

Because the witness did not observe who initiated the physical confrontation or the fatal shot, he cannot tell us who was the aggressor or where Martin and Zimmerman were positioned and what Martin was doing when Zimmerman fired the fatal shot. This missing information is important because, under Florida law, Zimmerman’s claim of self-defense must be rejected, if he was the aggressor, or if he was not in danger of being killed or suffering serious bodily injury when he fired the fatal shot.

For example, during the time period while the witness was in transit between locking his door, going upstairs, and looking out the window, Zimmerman, who outweighed Martin by 40 pounds, according to Wikipedia, might have locked his arms and legs around Martin, rolled over on top straddling him, and then pulled his gun out of the holster and fired the fatal shot. He might even have separated from Martin and fired the fatal shot. Neither scenario would justify using deadly force in self-defense.

Let us now consider what other forensic evidence to see what it might tell us about the relative positions of Zimmerman and Martin when Zimmerman drew his gun and fired.

What Can Forensics Add To This Investigation?

I would want to review the autopsy report and interview the medical examiner who conducted the autopsy to find out whether he noticed any injuries other than the fatal gunshot. For example, did Martin have any abrasions on his hands and fingers.

I would have a lot of questions for the medical examiner regarding the nature of the gunshot wound and Martin’s clothing.

For example, the weapon was a black Kel Tek 9 mm PF9 semiautomatic. The bullet would have been discharged when Zimmerman pulled the trigger causing the hammer to strike the primer igniting the smokeless powder in the casing producing rapidly expanding gas (consisting of carbon monoxide, nitrogen dioxide, carbon dioxide and other gases) that ejects the bullet, burning and unburned gunpowder (the burn always is incomplete), and trace amounts of the primer that contains heavy metals, including lead, antimony, and bismuth. Depending on the nature of the wound and the presence of all, some, or none of these materials, a qualified forensic firearms expert can determine how far away the gun barrel was when the shot was fired.

The gases, including the heavy metals, and some smoke from unburned but gaseous carbon, are projected only a few inches. The effects of the gas produce what are called contact or near-contact wounds that are characterized by variable skin lacerations or tears from the expanding gases that rip the skin apart and stippling, which is blackening skin from the unburned smokeless gunpowder that is propelled out the barrel of the gun with the bullet by the rapidly expanding gas.

As the distance of the gun barrel to the skin increases, the effect of the gas diminishes and only the unburned powder and bullet are capable of penetrating the skin. Stippling is present when the gun barrel is 0.5 centimeter to 1 meter from the wound. The pattern gets larger as the distance increases. So-called distant wounds do not cause tearing or stippling.

Based on Zimmerman’s statement, I would expect Martin to have had a contact or near contact wound with skin laceration or tearing caused by the explosive gases entering the wound expanding and tearing the skin. I also would expect to see some stippling or unburned smokeless powder. If I did not see evidence of either in the wound or clothing fibers, I would conclude that the gun barrel was more than a meter away, which is at odds with Zimmerman’s statement in which he claimed that he shot Martin as Martin was on top and hitting him.

Given Zimmerman’s statement, I also would expect to see high velocity blood spatter (mist-like spray of blood drops about 1 mm in diameter) or blowback on the barrel of Zimmerman’s gun, his shooting hand, and the sleeve of his jacket.

Absence of skin tearing, stippling, and high velocity blowback or blood spatter would seriously undermine a claim of self-defense.

2 Responses to Trayvon Martin: What Forensics Can Tell Us

  1. Pat Willis says:

    I have been consistently researching this case for any official updates. I did find the official autopsy report to be quite revealing. Trayvon Martin if reported to have one 1/4″ abrasion to the left ring finger and a gunshot would to the left chest which severed a ventricle. There was no exit wound. No other injuries were reported. No signs of any physical alternation with Zimmerman. It’s unrealistic to hypothesize that Zimmerman did not attempt to use his hands or arms to defend himself against what he alleges was an initial body contact by Trayvon Martin.

    Too many documentary forensic programs detail attacked, but still alert, individuals will use their arms, hands, finger, and fingernails to ward off an attacker. Thus, leaving DNA under the fingernails of attack victims, plus, DNA from the attacker around or in the wounds of those attacked. Why is it that Zimmerman has not presented any proof whatsoever that he as actually physically attacked by Trayvon Martin? Not even an official medical report from an ER the night of the alleged attack. In fact, a recorded conversation between an on the scene police officer and paramedic dispatch has Zimmerman refusing to be transported to an ER for physician treatment. The police officer cancelled that vehicle.

    The range of distance shooting Trayvon Martin has been stated by the media to be intermediate. For a Kel Tec PF9 that means a distance of 25′. I also researched the distance ranges of accuracy for an experienced shooter of a Kel Tec PF9. The shooter was a police officer reporting on range firing that particular firearm. I discovered the PF9 is rather accurate at 50 feet. Intermediate/mid range would then be 25′. Accuracy occurred with 3 shots placed in the same paper target area (right chest) at 10′, which is close range. Any range capable of leaving power burns on a victim’s clothing is considered point blank. That could be 3′ or less.

    I have found Zimmerman’s frequent story changing, whichever way the wind blows, as quite damaging to his credibility leaving him a zero value for credibility from the onset. The first severely incredible story began with the police incident reports, the night of shooting, stating that Trayvon Martin lay face down on the ground, which would have been impossible had he been straddling Zimmerman as Zimmerman alleged. He could only be face down landing face down on Zimmerman if shot by Zimmerman while be allegedly straddled by Trayvon Martin. That means heavy blood staining the front of Zimmerman’s clothing. Unfortunately for Zimmerman, he had no signs of heavy blood staining on his clothing approximately 30 minutes later, in front of the police garage surveillance camera. In fact, Zimmerman had no signs of his own blood on his clothing from all those alleged injuries he said bled profusely – back or front.

    In fact, there were no injuries apparent. I was able to use a large screen to view what was stated to be the original copy of a police video aired by the media, with ABC coming up, many days later, with altered video of a “head wound”. Then came up with another days later completely different than the first altered video. The other “head wound” had mysteriously disappeared with the second altered video.

  2. stobberdobber says:

    What do you have to say now? I noticed that there aren’t many comments here. As to your blow back why would there be much since the shot was to the heart and the bullet would cauterize the wound as it went in. You may have been a lawyer but you certainly are not a forensic expert or an audio forensic expert either. Your previously mentioned experts are full of themselves also. I have conducted much research on both of these so called experts, but mainly on Owen and his new software. He says that even though there is such a huge difference in the circumstances of the voice samplars there should be a 90+ percentage match.and cites the DAvalloo case as an example when in fact the Davallo had only a 68% match using this same software and there was not such an extreme pitch to the voices he compared in that case. Homework on your experts can do wonders to keep from getting egg on your face.

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