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Finding from study below: “Crime scene evidence was a consistent predictor of arrest across all crimes, but a very low percentage of arrests actually had physical evidence examined before the arrest.”

I was a new police officer in field-training (fresh from the academy). I and an older-experienced officer went to the scene of a burglary. The home owner asked if we were going to collect fingerprints. The training officer turned to me and asked me to dust and collect prints.

I gathered my evidence collection kit and carefully dusted and lifted prints from the point of entry while the experienced officer went to adjacent homes and made inquiries.

After working for about 30 minutes I was very proud of myself for the quality of my investigative work. The home owner seemed equally impressed.

We drove off and went to a park where the experienced officer asked to see my fingerprint cards. He offered some suggestions as to my evidence collection procedures and then proceeded to a trashcan and discarded my work.

I was appalled. He explained that the crime lab was overwhelmed with high-priority violent cases and wouldn’t have the time to process fingerprint cards for a burglary. He told me that I gained valuable experience and the home owner was happy so it was a win-win situation for all concerned.

This experience taught me that the criminal justice system was filled with limitations and priorities had to be observed. This was decades ago.

From the research below from the US Department of Justice, there seems to be little change in the collection and processing of forensic evidence from crime scenes. During vast majority of criminal investigations (except homicides and rapes) evidence is either not collected or processed by a crime lab.

The study

The study is based on pooled data for various crimes from five sites. The study explored the effect of forensic evidence on five different case outcomes, including: (1) whether a reported crime incident resulted in an arrest, (2) whether a case arrest was referred to the DA (3) whether an arrested suspect(s) was formally charged, (4) whether a prosecuted defendant was convicted, and (5) sentence length for incarcerated offenders.

Conclusions

In spite of the increased attention paid to forensic evidence over the past decade, there is little published empirical data identifying the types of evidence routinely collected, and the extent to which this evidence is submitted to and examined in forensic crime laboratories.

There is even less research that describes the role and impact of such evidence on criminal justice outcomes. While the current study shows that forensic evidence can affect case processing decisions, it is not uniform across all crimes and all evidence types; the effects of evidence vary depending upon criminal offense, variety of forensic evidence, the criminal decision level, and other characteristics of the case. The current study attempted to fill this gap in knowledge by examining the role and impact of forensic evidence on five felony crimes across five jurisdictions.

Given the varied nature of the criminal offenses, as well as contextual differences across study sites, the project reached the following conclusions:

1. The study data revealed that the collection of forensic evidence from crime scenes (and victims) was very extensive in homicides and, to a lesser extent, rapes; it was much more limited for assault, burglary and robbery offenses.

2. With the exception of homicides (89%), few of the reported crime incidents had forensic evidence that was submitted to crime laboratories. While the rate of submission of evidence for rape was 32%, submission rates in assaults, burglaries and robberies were under 15% of reported offenses.

3. With the exception of homicides (81%), the overall percent of reported crime incidents that had physical evidence examined in crime labs was low. Less than 20% of rape cases and less than 10% of assault, burglary and robbery incidents had lab examined evidence. Of evidence submitted to labs, however, rates of examination, with the exception of rape cases (58%), exceeded 70%. Consequently, it is clear that criminal justice officials external to the laboratory screen much of the forensic evidence and have a major influence on evidence examination priorities and practices.

4. The most frequently collected, submitted and examined forms of evidence were fingerprints, firearms and biological (blood and semen). For the sites included in this study and for the time period reviewed, DNA testing was rarely performed across all offenses and was concentrated in homicides and, to a lesser extent, rapes.

5. Although rates of arrest and conviction in study sites were low, the study rates were quite similar to national arrest and conviction data.

6. Rates of arrest, prosecutor referral, charging and conviction for the crimes of aggravated assault, burglary, and robbery with and without physical evidence were all substantial and statistically significant. For the crime of rape, differences were significant for all decision levels except for prosecutor referral.

7. Crime scene evidence was a consistent predictor of arrest across all crimes, but a very low percentage of arrests actually had physical evidence examined before the arrest. The exact role played by forensic evidence at investigation and prosecution levels is complex and dependent upon many factors.

8. Post-arrest, the predictive power of forensic evidence varied by crime type and criminal justice outcome. Lab examined evidence was a significant predictor of case charges for aggravated assault and rape. Forensic evidence also was associated with sentence length for assault and homicide. None of the measures of forensic evidence, however, were significant predictors of case conviction regardless of crime. In fact, few independent variables predicted trial/plea outcome due to the very high rate that charged cases resulted in conviction.

9. While collected forensic evidence was a consistent predictor of arrest across all offense types, most other predictors of criminal justice outcomes were typically non-forensic, legal and situational variables: victim and witness reports, victim/suspect relationships, victim medical treatment, and arrest methods.

10. Very few reported crime incidents had forensic evidence that linked a suspect to the crime scene and/or victim (~2% of all cases, 6% of cases with crime scene evidence, and 12% of cases with examined evidence). However, the conviction rate for the cases with linking forensic evidence was significantly higher than cases without such evidence. Furthermore, conviction rates were higher for offenses with two or more forms of individualizing evidence that associated offenders with crime scenes.

Source: http://www.ncjrs.gov/pdffiles1/nij/grants/231977.pdf.