Problems With Zimmerman’s Affidavit of Probable Cause

I downloaded the Affidavit of Probable Cause for George Zimmerman and read it with some interest. Several things are clear from this document:

1. No new evidence is mentioned. Pretty much everything referenced is stories and “facts” that have already made it into the media.

2. The State Attorney cherry-picked the “facts” and witness statements (as we know about them) and included only those that reflected badly on Zimmerman’s actions–even when those statements were contradicted by other facts and other statements. In other words, the least credible “witness” statements were used to put together this story. For example, the Affidavit includes statements from Martin’s girlfriend that were taken weeks after the incident as well as takes Martin’s mother’s word that the calls for help were from her son despite at least one impartial eye-witness whose statement directly contradicts that.

3. The Affidavit contains errors of fact. Specifically:

  • The Affidavit states that “The police dispatcher informed Zimmerman…to wait for the officer”. This is factually not true. The dispatcher asked Zimmerman if he wanted to meet the officer, and he said yes. This is directly from the 911 call and NOT  subjective.
  • The Affadavit says that “When the police dispatcher realized that Zimmerman was pursuing Martin, he instructed Zimmerman not to do that…”. This is factually not true. We’ve all heard the recording, and the dispatcher clearly only says, “We don’t need you to do that.” That is not an direct instruction to stop.
  • The Affidavit continues, in the same sentence, to state that “and that the responding officer would meet him.” This is factually not true. See the first bullet point under this item.

4. The Affidavit draws conclusions from facts rather than presenting facts; some of those conclusions are unsupportable. For instance:

  • The Affidavit states “Zimmerman…assumed Martin was a criminal.” Not exactly. Zimmerman thought Martin looked suspicious, which is not the same as saying he assumed that Martin was a criminal. An attorney ought to know the difference. The Affidavit also later states that Zimmerman “didn’t want the person he falsely assumed was going to commit a crime to get away…”
  • The Affidavit also states that Zimmerman continued to follow Martin after the dispatcher said it was not necessary, which has never been proven and is in fact a bone of contention in this case.
  • The Affidavit states that “Zimmerman confronted Martin”. This, too, has yet to be proven.

5. The Affidavit omits important details, such as Zimmerman’s injuries. I don’t know if the Affidavit is required by law to include details that contradict the “story” that the State is presenting, but it seems like Zimmerman’s injuries are relevant to the case. Strange.

Overall, this looks to be a pretty weak case. The most “damning” elements presented in this Affidavit are contradicted by, in my opinion, much more reliable evidence collected at/around the time of the incident.


CNN Backtracks on the Voice Analysis


An article posted to yesterday evening contains some interesting information and massive backtracking on the recent voice analysis on the screams heard the night Trayvon Martin died.

First, Tom Owen, the “expert” who performed the computer analysis of the voice samples, now says that only a 60% characteristic match not 90% is required to determine if two samples match:

“Using [his software], he found a 48% likelihood the voice is Zimmerman’s. At least 60% is necessary to feel confident two samples are from the same source, he told CNN on Monday — meaning it’s unlikely it was Zimmerman who can be heard yelling.”

Here’s what Owen said in a March 31, 2012 article in the Orlando Sentinel:

“”I took all of the screams and put those together, and cut out everything else,” Owen says.

The software compared that audio to Zimmerman’s voice. It returned a 48 percent match. Owen said to reach a positive match with audio of this quality, he’d expect higher than 90 percent.

“As a result of that, you can say with reasonable scientific certainty that it’s not Zimmerman,” Owen says, stressing that he cannot confirm the voice as Trayvon’s, because he didn’t have a sample of the teen’s voice to compare.”

Quite a change in two days. Now it is just “unlikely” that it was Zimmerman, not “certainly not”  Zimmerman. Updated to add: It has been pointed out to me that the word “unlikely” was the CNN reporter’s term, not Owen’s, and that is a fair point. However, the point still stands that Owen first said that because the “high quality” samples did not show greater than a 90% match, it was “reasonable scientific certainty” that the screams were not Zimmerman, and two days later said that only 60% is necessary for a match.

The CNN article goes on to acknowledge:

“And standards set by the American Board of Recorded Evidence indicate “there must be at least 10 comparable words between two voice samples to reach a minimal decision criteria….But that board’s current chairman Gregg Stutchman — who described Owens as a friend and well-respected in their field — said that exact metric doesn’t necessarily apply to the software Owens used.”

I’m glad they are addressing the issue of the number of words, but the article does not say why it does matter for Owen’s software. The article also doesn’t address the other problems with the samples. Still, it’s a start. And there’s more backtracking after that:

“David Faigman, a professor of law at the University of California-Hastings and an expert on the admissibility of scientific evidence, said courts and the overall scientific community have mixed opinions about the reliability of such “voiceprint” analysis.”

Of course, the reporter can’t quite let go without one final dig:

“Still, [Mr. Faigman] said, it wouldn’t be too hard for Zimmerman’s attorneys to find an audio expert to offer an opposing opinion.

“These expert witnesses come out of the woodwork when money is concerned,” he said.”

I find that quite ironic since I’ve read–but not confirmed–that the Orlando Sentinel paid for the original voice analysis. Out of the woodwork, indeed.

UPDATE: CNN has now updated the article. New link to article. In particular, the section regarding the questionable voice analysis has been expanded:

“But CNN and HLN legal analysts Beth Karas and Sonny Hostin raised questions about what the public should consider regarding the conclusions reached.”

This was followed by some discussion which concluded with both analysts “urging caution” in drawing any conclusions from the results of the voice analyses. Please go read! And Mr Owen has provided a non-explanation of why we should believe his software:

“Owen said the published American Board of Recorded Evidence standards apply only partially to the kind of test he conducted.

“These standards apply to the older aural-spectrographic analysis and software,” Owen said. “This only partially applies to the biometric software.”

Backwards and backwards and backwards…

More on Tom Owen’s Voice Identification

Let’s look at what another expert has to say about comparing someone speaking in a normal voice to someone screaming. This information comes from from Steve Cain. A little bit about him:

“Cain is president of Applied Forensic Technologies International of Chicago and Lake Geneva, Wisconsin, which specializes in voiceprint and audio tape analysis, tape authentication, polygraph examinations and analysis of questioned documents. He has more than 25 years experience in forensic science, including service as an agent in both the U.S. Secret Service and Internal Revenue Service. He was chief of the voiceprint units and senior document examiner for both the Secret Service and IRS as well as chief polygraph examiner for the IRS, with extensive courtroom testimony experience, including California’s notorious Hillside Strangler case.”

In an article that he wrote, called The Use of Voice as a Forensic Tool, he explicitly states:

“…it’s essential that speech samples contain exactly the same words and phrases as those in the questioned sample, because only identical speech sounds are used for comparison. “

So again, I ask how Tom Owen could possibly have made a credible determination about who was screaming from the voice samples he had available. Answer: He cannot.

Updated: has an excellent article up about Tom Owen, his software, and possible conflicts of interest.

Voice Identification Experts’ Work Debunked

So the news this morning is that two supposed experts in voice identification have concluded that the screaming voice on the 911 calls is not George Zimmerman. A story on MSNBC reads:

“Tom Owen, forensic consultant for Owen Forensic Services LLC and chair emeritus for the American Board of Recorded Evidence, told the Sentinel that he used voice identification software to rule out Zimmerman.”

In this case, the expert compared Zimmerman’s first call to the police’s non-emergency line with the screams heard on another call made to the 911 line.

Curious about the standards for voice identification, I looked up the American Board of Recorded Evidence’s guidelines for reliable and accurate voice identification. The name of the document is “American Board of Recorded Evidence – Voice Comparison Standards” and the first paragraph of the document reads, in part, “This document specifies the requirements of the American Board of Recorded Evidence for the comparison of recorded voice samples. These standards have been established for all practitioners of the aural/spectrographic method of voice identification…”

This document discusses the importance of duplicating the recording conditions–including microphone, transmission system, acoustic environment, etc–and speech delivery–including repetition, speech rates, stresses, etc. A casual reading of these guidelines will see that there are already problems with comparing voices recorded on separate types of phones, recorded on different pieces of equipment, and with the subject under different speaking conditions (casual vs fighting/stressed).

However, here are the real smoking guns, where the supposed expert’s claims are shot down:

5.2 Verbatim/Non-verbatim. The known, or another unknown voice sample, must be either wholly verbatim (preferred), or partially verbatim to allow meaningful comparisons with unknown voice samples. A partially verbatim sample should include phrases and sentences containing at least three (3) similar, consecutive matching words…”

When one sample consists only of “Help” or “Help me”, there cannot be 3 similar phrases between Zimmerman’s non-emergency call and the 911 tapes.

5.3 Number of Comparable words. There must be at least (10) comparable word between two (2) voice samples to reach a minimal decision criteria. Similarly spoken words within each sample can only be counted once. It is noted that in most voice samples at least some of the words identified at this point will not be useful in the final examinations.”

Again, when one sample consists of one or two words total, this criteria cannot be met.

“5.4.1 Disguise. Samples, or portions of samples, that contain falsetto, true whispering (in contrast to low amplitude speech), or other disguises that obviously change or obscure the vocal formants or other speech characteristics, may need to be eliminated from comparison consideration…”

I think that screaming for one’s life could be considered something that would change or obscure one’s normal speaking patterns.

And of course the final nail in the experts’ claims:

5.4.6 Variations between samples. Though the following variations can quickly end a voice comparison, the problem can often be remedied by obtaining additional known samples:

a. Transmission systems. Normally, samples being compared should be produced through the same type of transmission system, for example, the telephone, a microphone in a room, or a RF transmitter/receiver. If aurally or spectrally the samples are noticeably different due to the dissimilarities in the transmission systems and filtering does not rectify these differences, no further comparisons should be made.

b. Recording systems. Normally, samples being compared should be produced on either good quality, or compatible, recording systems. However, if the recordings contain uncorrectable system differences that affect aural and spectral characteristics, no further comparisons should be made. Examples of recording differences that can affect the results include high-level flutter, gross speed fluctuations, and voice-activated stop/starts.

c. Speech delivery. Normally, samples being compared should have the speakers talking in the same general manner, including speech rate, accent, similar pronunciation, and so on. However, in cases where this has not been done, as in poorly produced known exemplars, no further comparisons should be made.

d. Other. Any other differences between the voice samples that noticeably effect aural and spectral characteristics should be closely reviewed before proceeding with the examination.”

I submit that the differences between Zimmerman’s non-emergency call and the later 911 call make any comparison of the two samples meaningless. I encourage readers to read the guidelines for themselves.

“Self-Appointed” Watch Captain Claim Debunked

Several news sources have labeled George Zimmerman a “self-appointed” Neighborhood Watch block captain. Guess what? That’s not true.

One of the other residents of the gated community is on record stating that is false. Frank Taafe, a “neighbor of George Zimmerman and fellow neighborhood watch captain” told NBC News that “Zimmerman was appointed as a watch captain, despite reports that he appointed himself to the post.” I’d think Zimmerman’s co-captain would know best, wouldn’t you?