Program Profile: DNA Field Experiment

This was an experiment to evaluate the impact of deoxyribonucleic acid (DNA) evidence collection and testing on the investigation of high-volume property crimes. The program is rated Effective. Across five sites, more suspects were identified, arrested, and prosecuted in the treatment group cases, compared with suspects in the control group cases. These differences were statistically significant.

An Effective rating implies that implementing the program is likely to result in the intended outcome(s).

This program's rating is based on evidence that includes at least one high-quality randomized controlled trial.

This program's rating is based on evidence that includes either 1) one study conducted in multiple sites; or 2) two or three studies, each conducted at a different site. Learn about how we make the multisite determination.

Program Goals

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.)

Program Components

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 person who committed the offense 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 persons. 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 United States. CODIS has three hierarchal components: National DNA Index System (NDIS), State DNA Index System (SDIS), and Local DNA Index System (LDIS). NDIS is run by the Federal Bureau of Investigation, while SDIS and LDIS are run by States. These databases hold a vast array of forensic information, including information on unidentified human remains, profiles of the person who committed the offense, and various forensic information from crime scenes, with indices organizing all information. After evidence is collected and entered in the database and a hit is found, a suspect can be identified. The State crime lab then sends the information to the local crime lab, which then forwards that information to the police department.

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.

Key Personnel

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.

Study 1

Roman and colleagues (2008) conducted a randomized experiment to evaluate the effectiveness of deoxyribonucleic acid (DNA) evidence on cases at five sites: Denver, Colo.; Orange County, Calif.; Phoenix, Ariz.; Los Angeles, Calif.; and Topeka, Kan. The study attempted to collect biological evidence from scenes of approximately 500 property crimes from each site, with 250 randomly assigned to a treatment group and 250 to a control group. Due to implementation issues, each site did not end up with exactly 250 treatment and 250 control cases. Each site differed slightly in protocol for evidence collection and analysis, but followed the same basic procedure.

The precise periods in which evidence was collected varied across the five sites, but all evidence was gathered between November 2005 and July 2007. In regard to number of cases for each site, Denver had 255 in the treatment group and 255 in the control group; Orange County had 249 in the treatment group and 248 in the control group; Phoenix had 251 in the treatment group and 257 in the control group; Los Angeles had 193 in the treatment group and 198 in the control group; and Topeka had 131 in the treatment group and 129 in the control group.

The DNA evidence for cases in the treatment groups received immediate and efficient DNA processing, combined with traditional law enforcement processing. The comparison group was designed to have case outcomes that resulted solely from traditional investigation. Therefore, the DNA evidence for cases in the control groups was not processed for at least 60 days, and these cases were processed using traditional procedures. This was based on the assumption that an outcome in the case would be reached before the end of the 60 days and the DNA was processed. Thus, any difference in outcomes between groups could be attributed to the DNA evidence.

Three evaluation outcomes were used as measures of effectiveness: 1) Whether a suspect was able to be identified for the case, 2) whether an arrest was made in the case, and 3) whether the case was referred to prosecution. Data was obtained from each police department and maintained in a Microsoft Access database. Analysts then measured the percentage of cases that met all these outcomes for both the treatment and control group, and results were then compared against each other.

The overall outcomes were examined, and were also broken down by site due to differing procedures. The total sample size with all sites combined was 1,079 for the treatment group, and 1,081 for the control group. The study authors conducted subgroup analyses on the five individual sites separately and on individuals’ criminal history, types of evidence collected, and who collected the evidence.

The deoxyribonucleic acid (DNA) collection process can incur many costs, including labor costs, use of technology, training, lab analysis, and other various expenses. Roman and colleagues (2008) conducted a cost-effectiveness analysis for the use of DNA evidence in addition to their effectiveness evaluation to compare relative costs to relative outcomes. They found that across all sites combined, using DNA evidence to process a single case added approximately $1,400 in costs.<br><br> They also found that, for suspects who would not have been identified and arrested through traditional investigations, the use of DNA testing cost $4,502 for each additional suspect identified and cost $14,169 for each additional arrest. The researchers noted that these costs were not the expected cost per suspect identified, arrested and prosecuted but rather represented the added expense of identifying, arresting and prosecuting burglars who otherwise would not have been caught. Costs varied by site depending on different procedures.

Due to the sensitive nature of deoxyribonucleic acid (DNA) evidence, crime scene personnel had to undergo extensive training to ensure biological materials were preserved and handled properly. They were trained on how to properly identify, collect, and process biological evidence at property crime scenes to avoid contaminating the evidence. They also were trained on what types of evidence they were allowed to collect and when they needed to call a crime scene investigator to collect certain types of evidence.

Subgroup Analysis

Roman and colleagues (2008) conducted separate subgroup analyses on the following five sites to evaluate the effectiveness of deoxyribonucleic acid (DNA) evidence: 1) Denver, Colo.; 2) Orange County, Calif.; 3) Phoenix, Ariz.; 4) Los Angeles, Calif.; and 5) Topeka, Kan.

In Denver, Los Angeles, and Phoenix, the study authors found that a greater number of treatment group suspects had been identified, arrested, and prosecuted, compared with the control group suspects. These differences were all statistically significant. In Orange County and in Topeka, treatment group suspects were identified in statistically significant more cases than the control group suspects. However, in both sites, there were no statistically significant differences between groups in number of arrests or number of cases accepted for prosecution.

Additional Outcomes

The study authors also looked at several other outcomes, including criminal histories, types of evidence collected, and who collected the evidence. They found that 1) DNA was at least five times more likely to result in a suspect’s identification, compared with fingerprints; 2) suspects identified by DNA had at least twice as many prior felony arrests and convictions, compared with those identified by traditional investigation; and 3) blood evidence resulted in better case outcomes, compared with other biological evidence, particularly from items that had been handled or touched. These differences were all statistically significant. However, there were no statistically significant differences between forensic technicians and patrol officers in collecting biological evidence that would result in suspects’ identification.

These sources were used in the development of the program profile: