The purpose of the study was to:
Estimate the percentage of crime scenes from which one or more types of forensic evidence are collected.Describe and catalog the kinds of forensic evidence collected at crime scenes.Track the use and attrition of forensic evidence in the criminal justice system from crime scenes through laboratory analysis, and then through subsequent criminal justice processes.Identify which forms of forensic evidence contribute most frequently to successful case outcomes.
The study called for tracking cases and forensic evidence through local criminal justice processes for five offenses: homicide, sexual assault, aggravated assault, robbery and burglary. Two sites, Denver, Colorado, and San Diego, California, were selected for this portion of the study. Researchers obtained detailed information on 4,049 offenses in Denver and 3,207 offense in San Diego. Demographic data were collected on victims (Victim Data n = 7,583) and defendants (Defendant Data n = 2,318). Data on forensic evidence collected at crime scenes included DNA material (DNA Evidence Data n = 1,894), firearms evidence (Ballistics Evidence Data n = 488), latent prints (Latent Print Evidence Data n = 766), trace evidence (Other Impressions Evidence Data n = 49), and drug evidence (Drug Evidence Data n = 43).
Data collection procedures:
Denver: The Denver Police Department maintains a records management system with data on all major crimes reported to the police. The department's crime lab has a commercial laboratory information system in which forensic analysts entered the results from analysis performed on evidence from crime scenes. The district attorney's office also has a management system for support to the attorneys on cases accepted by the office. The system includes the crime report number assigned by the police department and tracks the progress of cases. After selecting a crime, the police system was queried to obtain basic data about the offense. Inquiries were then made into the district attorney's system to determine whether an arrest had been made. Finally, the crime lab's system was accessed for information on evidence collected and the results of analysis by forensic analysts. With the help of personnel from key agencies, researchers developed an Access database to capture the information about each selected case.San Diego: The San Diego Police Department maintains a Criminal Records Management System (CRMS) which includes information on all crimes reported to the police, including whether evidence was collected and whether arrests were made by investigators. The District Attorney's office maintains a case management system that provides information on defendants. Through the case number from the police department, defendant data was merged with the other data collected for this study. As in Denver, researcher developed an Access database to capture the information collected for each case.
In Miami-Dade County, Florida, the study focused on an experiment that had been underway by the crime lab on processing DNA evidence from no-suspect, unsolved property crime (Miami-Dade County Data n = 1,421). The objectives of the experiment were to determine whether processing times could be reduced and whether the reductions, in fact, lead to increased arrest rates for the offenses. Working with the Marshall University Forensic Science Center (MUFSC), the crime lab of the Miami-Dade County Police Department (MDPD) developed procedures to significantly reduce the overall time for processing DNA evidence. In February 2007, the crime lab began submitting these "Fast Track" samples to MUFSC on a monthly basis from recent no-suspect property crimes. Two comparison groups were included. The "Bode Cases" are from a National Institute of Justice (NIJ) grant awarded to the MDPD in 2003 for reducing the backlog of DNA evidence that had accumulated from property crimes. The "Slow Track" cases included DNA evidence sent by the crime lab to MUFSC in January 2007 from no-suspect property crimes that occurred between January and July 2006. Due to the age of these cases, the agreement was that the MUFSC would process the samples whenever forensic analysts in their lab had available time. The Fast Track cases were the primary focus because the objective was to analyze the DNA evidences from these case as quickly as possible. The overarching objective was to solve cases, and the expectation was for a higher clearance rate from the Fast Track cases than from the Bode and Slow Track cases.
Crime Lab Survey
To better understand the organizational arrangements and staffing for collection of forensic evidence, researchers conducted a survey of selected law enforcement agencies (Crime Labs Survey Data n = 75). Researchers determined that a telephone survey would be the most appropriate means of contacting personnel in the crime labs and contracted with the National Clearinghouse for Science, Technology and the Law (NCSTL) to provide staff for conducting the survey.
The samples for the Victim Data (n = 7,583), the Defendant Data (n = 2,318), the DNA Evidence Data (n = 1,894), the Ballistics Evidence Data (n = 448), the Latent Print Evidence Data (n = 766), the Other Impressions Evidence Data (n = 49), and the Drug Evidence Data (n = 43) were drawn from the relevant databases based on crime type at each site.
In Denver, Colorado, after a review of crime statistics, the final sampling plan was to code all homicide and sexual assaults over a 12-month period and a random sample of assaults, robberies, and burglaries over a 12-month period. The sampling percentages are approximately 38 percent for assaults, 27 percent for robberies, and 35 percent for burglaries. The starting points for these three categories were crime listing from which cases were randomly selected. The assaults and robberies were sampled from 2005 and burglaries were sampled from 2006.
In San Diego, California, the sample includes all homicide cases from 2005 and 2006, and all sexual assault cases from 2005. Samples for aggravated assaults, robberies, and burglaries were developed from crimes that occurred during 2005. For assaults, researchers randomly sampled 1184 case, of which 627 cases had forensic evidence. For robberies, the sample was 735 cases of which 322 cases had forensic evidence, and for burglaries 795 cases were sampled of which 460 cases had forensic evidence.
The sample for Miami-Dade County Data (n = 1,421) includes:
Fast Track Cases - evidence from 602 property crimes from January 2008 through July 2008;Slow Track Cases - evidence from 237 property crimes from January through July 2006; and Bode Cases - evidence from 582 property crimes from January 2005 through January 2006.
The sample for Crime Labs Survey Data (n = 75) was identified from the 2005 census of publicly funded crime labs conducted by the Bureau of Justice Statistics.
The universe for the major crimes cold cases includes all open homicide and sexual assault cases in Denver in 2005 and 2006, all open aggravated assault and robbery cases in Denver in 2005, all open burglary cases in Denver in 2006, all open homicide cases in San Diego in 2005 and 2005, and all open sexual assault, aggravated assault, robbery and burglary cases in San Diego in 2005. The universe for the Miami-Dade county data includes all no-suspect property crimes in Miami-Dade County, Florida between 2005 and 2008. The universe for the crime lab data includes publicly funded crime labs in the United States in 2005.
The Victim Data includes the following eight variables: case number, city, victim age, victim sex, crime type, burglary type, case disposition, and a unique record identifier.
The Defendant Data includes 19 variables on: city, age of defendant, sex of defendant, race of defendant, prior convictions, prior charges, prior filings, jail time, prison time, probation time, filed charge, final charge, crime date, arrest date, filing date, and disposition date.
The DNA Evidence Data includes 21 variables on: city, type of DNA evidence obtained, where the evidence was obtained from, quality of the DNA profile obtain, matches to other evidence, exclusion of evidence, dates of evidence collection, request for analysis and analysis report dates, crime type and clearance type.
The Ballistics Evidence Data includes 15 variables on: city; number of ballistics items; evidence description; gun shot residue (GSR) results; date of ballistics evidence collection, analysis and report; if the type of ammunition was successfully identified; match to other evidence; crime type; and clearance type.
The Latent Print Evidence Data includes 15 variables on: city, crime type, number of latent prints in the case, quality and description of the print, match to other evidence or exclusion indicator, date of evidence collection, analysis and report, and clearance type.
The Other Impressions Evidence Data includes 11 variables on: city, crime type, number of latent prints, description of print and quality, date of evidence collection, date of analysis and report, and clearance type.
The Drug Evidence Data includes 11 variables on: city, crime type, drug analysis found, drug paraphernalia found, drug items matched, date of evidence collection, date of analysis and report, and clearance type.
The Miami-Dade County Data includes 16 variables on: type of case, offense group, sample group, date of crime, date evidence sent to and returned from Bode/Marshall, notification date, date of case disposition, forensic hit, offender hit and disposition category.
Crime Lab Survey
The Crime Labs Survey Data includes 88 variables on if the agency has a crime scene evidence collection unit, who is responsible for collecting evidence, number of trained evidence collection specialists, types of personnel in the crime scene unit, types of crimes the crime scene unit collects evidence for, types of evidence collected by the crime scene unit, who other than a specialized crime scene unit collects evidence, what crimes they collect evidence for and the types of evidence they collect, who writes the crime scene report and who makes requests for analysis of collected evidence.
Crime Lab Survey Data: Of the 96 full-service labs contacted as part of the study, 75 crime labs provided information for a response rate of 78.1 percent.