Chain of Custody
As a part of the foundation for introduction into evidence of the results of any blood-alcohol test, the prosecution must establish a complete chain of evidence. In other words, the prosecutor must be able to trace, through competent evidence, exactly where the chemical sample was at all times, from when it was extracted from the defendant to the moment it was finally analyzed; in some instances, as, for example, with pre-trial discovery, the chain must be extended into the present. In addition to having to prove where the sample was, the prosecutor also will probably have to show in whose custody it was at all times and that it was properly labeled and stored. He must negate the possibilities that it was in an unidentifiable individual's control at any point in time and that the sample was misplaced or exchanged mistakenly for another sample. In short, the prosecution must clearly establish that the sample taken from the defendant was the one analyzed and could not have been tampered with.
Certainly, DUI Lawyers should always object to admission of the test results without a complete showing of chain of custody, if only to establish a record for appeal. Usually a number of individuals have handled the sample in question, among them the arresting officer, the medical technician or physician, the transporting officer, the individual in charge of evidence at the laboratory, and/or the laboratory technician or chemist. Counsel should insist on the testimony of each such individual or at least the testimony of a witness to the custody of the sample by the individual.
In addition to testimony of custody, the prosecution should be required to show that an accepted means of labeling the sample was used. Again, each jurisdiction varies in its requirements as to the labeling of evidence, and counsel should be familiar with them. Generally, however, the sample should have been labeled by the person who took the sample and at the time the sample was taken and placed in its container.
Assuming that the objection or motion to suppress is denied, however, the issue is far from dead. DUI attorneys should emphasize in his cross-examination and argument the failure of the prosecution to establish that the blood analyzed was, in fact, the defendant's. All of the testimony and legal presumptions concerning bloodalcohol concentrations mean nothing if it cannot be proven beyond a reasonable doubt that the blood analyzed was not taken from someone else.