Qualified expert testimony may be admissible by either side in a criminal trial in Tennessee when the trial court determines it may substantially assist the trier of fact in understanding the evidence or deciding a material issue. When determining whether scientific evidence is reliable enough to be of assistance, trial courts in Tennessee consider how the evidence has been tested, whether it has been subject to peer review, whether a rate of error is known, and whether it is generally accepted in the scientific community. It of course also must be relevant to be of assistance to the trier of fact. In the recent case of State v. Adams, M2014-00501-CCA-R3-CD (Tenn.Crim.App. 6-19-2015), the Court of Criminal Appeals affirmed a trial court ruling disallowing a DUI defendant's offered expert testimony concerning the effect of freon contamination of the blood on a preservative used to preserve a blood sample for testing alcohol content.
The defendant in the Adams case was convicted at trial of DUI, second offense. The state's evidence at trial included the results of forensic toxicology testing of a blood sample from the defendant. The state forensic expert testified that a blood preservative was used with the sample container so that accurate testing could still occur up to five years after the sample was taken. Without the preservative, the ethanol content would be lost over time.
The defendant happened to be a chemist. He had a co-worker who was a chemist as well, and sought to present the co-worker and himself as expert witnesses to testify that the defendant was in frequent contact with freon at work, which could lead to freon in his blood. According to the offered witness, freon in the blood could prevent the preservative from working.
The trial court did not find this testimony to be of any assistance in helping the jury decide the case. So it was not presented to the jury. The Court of Criminal Appeals affirmed that ruling, noting that the defendant did not offer evidence that there actually was any freon in the defendant's blood sample. Nor was there any evidence offered regarding testing, peer review, or scientific acceptance of the theory that freon would prevent the preservative from working or lead to an inaccurate result. In addition, if the defendant's offered theory was correct and there was indeed freon contamination which prevented the preservative from working, the result of the state's forensic testing would be less ethanol content in the sample than when the sample was taken ... not more.
For more information on when expert testimony may be admissible in a criminal trial, contact Hindman & Associates.