Chemical Defenses in Narcotics Cases

Technology and Chemical Analysis in Drug Crimes Defense

Counsel faced with defending a substantive drug prosecution is confronted with a two-witness paradigm: the agent and the chemist. It is virtually impossible to shake the testimony of an experienced agent. The methods used by prosecution analysts for drug identifications have evolved. Early methods were easily applied but proved to be invalid. Current methods are more technically sophisticated and may be valid in skilled hands. Even so, they are often improperly applied. However, the unjustified absolute confidence technicians express regarding the correctness of their conclusions remains unchanged.

The current favorite method among forensic analysts is mass spectrometry. The analyst compares the spectrum of the suspected drug with a standard or reference spectrum of the drug. If the spectra are sufficiently similar, the analyst testifies that in his opinion the suspected drug is the same compound as the reference sample.

Modern mass spectrometers contain computers. These computers incorporate spectral libraries containing spectra of hundreds of thousands of compounds. At a keystroke or mouse click, the spectrum of an unknown substance can be compared to each library spectrum. The operator is then presented with an ordered list of compounds whose spectra most closely match that of the unknown. Such lists generally include estimates of degree of match and the probability that the spectrum of the suspected drug is identical to one in the reference library. Crime laboratory analysts rarely use these computerized matches even though the search takes only a few seconds.

Technology now permits defense counsel to convert the spectra it receives in discovery to digital form. Using a laptop computer loaded with spectral libraries the defense is now able to compute the match probabilities which the prosecutions technician declined to evaluate. Frequently, these probabilities will create a reasonable doubt.

• Lawyer Prompts Drug Analyses