Deoxyribonucleic acid (DNA) stores the genetic code of the human body and is present in items such as blood, saliva, and hair. It is used to identify an individual’s genetic characteristics, and can be vital to the identification, arrest, and prosecution of a suspect in a crime. While DNA evidence has traditionally been used to investigate more serious violent crimes, it can also be useful in solving property crimes. The goal of the DNA Field Experiment was to examine the use of DNA evidence in the investigation of residential burglary, commercial burglary, and theft from automobiles, and its impact on the number of suspects identified, arrested, and convicted in these types of crimes compared to cases processed without DNA evidence.
DNA processing can be a lengthy and costly process, so another goal of the program was to evaluate the cost-effectiveness of DNA evidence in solving property crimes and to determine if the use of DNA evidence produced outcomes that were worth the costs of DNA processing. (Limits on resources are often an issue for using DNA evidence, so government funding was provided to several sites to conduct the evaluations.)
Biological evidence must be carefully collected, stored, and submitted to the crime lab to ensure a sample that can be analyzed for use in an investigation. Evidence must be handled properly to avoid decomposition or contamination; improper handling of a biological specimen can ruin its potential for analysis. DNA evidence can be collected from victims, suspects, their belongings, and from crime scenes. In burglaries, the perpetrator may leave behind a variety of biological material, including blood, saliva, and skin cells.
To create DNA profiles, biological material is entered into a computerized database, which can then be searched against samples from a specific suspect. DNA profiles from crimes can also be searched against DNA from convicted offenders. In addition, DNA profiles from different crimes can be compared against each other to assist in the investigation of linked cases.
Suspects are identified through the Combined DNA Index System (CODIS) database, a computer system that stores DNA profiles created by Federal, State, and local crime laboratories in the
Specific evidence-collection techniques were used to collect biological evidence from a burglary crime scene, including retracing the burglar’s steps and uncovering their motives, points of entry, and items touched. Evidence had to be collected carefully and quickly in order to get a good sample.
Once the evidence is collected, there is a lengthy and complicated process to analyze the sample. Stages in DNA processing include:
Preliminary testing. This component includes the initial examination of the sample, preparation of the test sample, and screening for the presence of human blood.
Generation of a DNA profile. DNA is extracted from the sample and genetic material is made into a profile.
CODIS entry. In this step, the DNA profile is recorded into the computerized system.
Case verification. The sample is confirmed using different databases (e.g., a local sample may be matched to a State database).
Investigation. The police department uses the evidence to locate, arrest, interview, and book a suspect.
Post-arrest procedures. Additional forensic lab resources are used to process a confirmation sample from the suspect after arrest.
The successful processing of DNA evidence from crime scenes requires a high level of collaboration between the police department, the crime laboratory, and the prosecutor’s office. Each agency has its own responsibilities, and relies on cooperation from the other agencies to make sure that the processing is done efficiently:
Police department. First, members of the police department—including officers, crime scene investigators, and detectives—are responsible for processing crime scenes and collecting evidence properly. They must then transport the evidence to the laboratory and maintain police records and databases.
Laboratory personnel. Members of the laboratory, including analysts and forensic technicians, are responsible for processing and analyzing the biological evidence in an efficient manner. They keep the police department updated on results of tests in order to assist the investigation; good communication must therefore be maintained between the two agencies.
Prosecutor’s office. Finally, the police department and crime laboratory must collaborate with the prosecutor’s office in order to provide evidence for the prosecution of a suspect. They are responsible for providing detailed reports and analyses in a timely manner, in order to assist with the case against the suspect. The prosecutor then has the burden of using this evidence to assist in arguments proving the suspect’s guilt.
The process from data collection to prosecution can be time sensitive and complex, and actors are required to collaborate in ways that are more complex than in routine criminal investigations. Therefore, good communication and cooperation among all actors involved are vital to the successful use of DNA evidence.
Roman and colleagues (2008) found that property crime cases where deoxyribonucleic acid (DNA) evidence was used resulted in more than twice as many suspects identified, twice as many suspects arrested, and more than twice as many cases accepted for prosecution, compared with traditional investigation.
Identification of Suspects
Across all sites. Suspects were identified for 31 percent of cases which used DNA evidence in the treatment group, compared to 12 percent of suspects identified in the control group. This difference was found to be statistically significant.
Arrest of Suspects
Across all sites. In the treatment group, which used DNA evidence, suspects were arrested in 16 percent of cases. In the control group, 8 percent of suspects were arrested. These differences were found to be statistically significant. The total number of arrests was 173 in the treatment group and 86 in the control group
Cases Accepted for Prosecution
Across all sites. For those cases in the treatment group, which used DNA evidence, 19 percent of cases were prosecuted. This compared to 8 percent cases accepted for prosecution in the control group, a statistically significant difference.
Denver. Forty-six percent of cases which used DNA evidence were accepted for prosecution in the treatment group, compared to 17 percent of cases accepted for prosecution in the control group. This difference was found to be statistically significant.
The researchers also looked at several other outcomes in their analysis, including criminal history of offenders, types of evidence collected, and what type of person collected the evidence. They found that:
· DNA is at least five times more likely to result in a suspect identification compared with fingerprints.
· Suspects identified by DNA had at least twice as many prior felony arrests and convictions as those identified by traditional investigation.
· Blood evidence results in better case outcomes than other biological evidence, particularly evidence from items that were handled or touched.
· Biological material collected by forensic technicians is no more likely to result in a suspect being identified than biological material collected by patrol officers.