Forensic Laboratory Independence, Control, and the Quality of Forensic Testimony
Abstract: The relationship between forensic laboratories and the other institutions of law enforcement varies widely over space and time in the United States. Some jurisdictions have their own local lab within the police department, some locate the lab within the district attorney's office, others depend on a statewide lab system either independent or under the state police, and others still contract with a private lab to process their forensic evidence. These different organizational forms may shift the incentives lab technicians and managers have to provide timely and accurate analysis and testimony. In this paper, I investigate how the relationship the forensic lab bears to the rest of the structure of law enforcement correlates with the quality of forensic analysis and testimony in a sample of trials that eventually led to convictions and, later, exonerations. Both within evidence types and across all evidence types, the expert prosecution testimony provided by employees of public crime labs is consistently worse than expert prosecution testimony given by employees of private forensic labs working under contract for the state. These results are robust to controlling for case characteristics, defendant characteristics, time trends, and state fixed-effects. Furthermore, there do not seem to be significant differences among public crime lab types: validity rates for crime labs controlled by the local police are similar to those controlled by the state police and to those that are independent from the police, suggesting the dictating formal independence may not be enough to insulate public lab from whatever forces are driving their poor performance.
