by Roger Koppl
Most people think DNA evidence is bulletproof. Molecular biologist and forensic scientist Dan Krane has very nice presentation on some of the problems that can arise in this area. When the biological sample is mixed, degraded, or small, the evidence can be ambiguous, which allows subjective judgment to enter. Recent events in Baltimore point to another problem that has nothing to do with such ambiguity.
On September 27th, the Baltimore Sun reported, “In at least nine homicide, sex assault and burglary cases, Baltimore police detectives instructed crime lab technicians not to follow up on convicted criminals’ DNA found on evidence at crime scenes because they determined it was not relevant to their investigations.” The police have a plausible explanation. “Police spokesman Sterling Clifford played down the significance of the discovery, saying detectives routinely make judgment calls on evidence.” Moreover, says Clifford, “Very often those crime scenes are enormous, sometimes covering entire city blocks.” Read the rest of this entry »