Last week, Judge Nelson granted a defense motion, which sought to exclude the testimony of two witnesses who were prepared to testify that screams heard in a 911 call belonged to Trayvon Martin. This was a huge blow to the prosecution. The screams allegedly were screams for help. The testimony would have helped the prosecution because if Trayvon Martin were screaming for help, Mr. Zimmerman could not have believed that he himself was in danger, thus negating his self-defense argument.
The two witnesses the State sought to examine at trial are experts in the field of voice recognition. They would have testified that they performed scientific tests on the 911 recording and were able to determine as a result of those tests that the screams were those of Trayvon Martin. The defense objected that the tests used to analyze the recordings are not techniques which are generally accepted within the scientific community. The Judge agreed.
The Frye Rule
Known as the Frye Rule, the rules of evidence provide that expert witnesses may testify about tests performed only if the tests are those which the scientific community accepts and uses. The Judge noted in her decision that there are currently three employed methods of voice identification:
- Auditory phonetic analysis
- Acoustic-phonetic analysis
- Gaussain Mixture Model analysis
The Judge ruled that the tests had not been “sufficiently tested and accepted by the relevant scientific community” and that testimony about these tests would therefore confuse issues and mislead the jury.
This week Zimmerman is supposed to recount his description of the events to the jury. We will be tracking this case as it progresses.