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This section will address some of the most frequently raised issues related to forensic evidence as it is used to prepare for and conduct a criminal trial.  When possible, links to authoritative literature on the subject will be provided.  

Crime Scene to Courtroom - what does this mean?
Laboratory staff ask too many questions.
Who determines what evidence should be tested by a laboratory?
Evidence Triage - is this something new?
Shouldn't prosecutors determine what evidence is probative or not?
Lawyers are not scientists.  How do they know what tests should be conducted?
Thanks to shows like CSI, juries expect every piece of evidence to be tested.
Scientists are sometimes unavailable due to illness or retirement.


Crime Scene to Courtroom - what does this mean?
The management of forensic evidence, whether it's ever tested in a laboratory or not, is a systematic process that starts at the scene of a crime, but does not end until a criminal matter has reached its final disposition.  For the entire system to be effective, an appropriate degree of expertise is needed among those individuals involved in the process.

Over time, mostly because of the retirement or promotion of technically trained personnel, expertise across the crime-scene-to-courtroom spectrum is lost and must be quickly replaced.  Sometimes the sheer volume of cases managed by prosecutors and judges make it especially challenging to commit the time needed for a thoughtful approach to scientific evidence.  But rest assured, the time wasted by not properly managing or understanding the nuances of forensic evidence is far more costly in the long run.

Typically, it is the forensic laboratory scientists themselves who are in the best position to deliver the training and continuing education that is needed to fill these gaps.  When expertise across the system is lost, the typical reaction is to "dump" large volumes of evidence on forensic laboratories with the expectation that the crime lab folks will sort everything out.  Too often, this approach results in the submission of low-value evidence and creates bottlenecks that lead to high laboratory backlogs and delayed justice for both victims and defendants.

Recommended Reading

Transforming Practice Through Competency Building (2002)

Improving Forensic Death Investigation (2011)

Crime Scene Investigation: A Guide for Law Enforcement

Crime Scene Investigation: A Reference for Law Enforcement Training

Death Investigation: A Guide for the Scene Investigator

Untested Evidence: Not Just a Crime Lab Issue

Forensic Resources on the Web

Federal Judicial Center's Reference Manual on Scientific Evidence (2000)


Laboratory staff ask too many questions.  I wish they would just do what I ask.
Curiosity is a common attribute of scientists.  So too is a desire for efficiency.  In the vast majority of cases submitted to our forensic laboratories, evidence is accepted and processed with no questions asked.  Police departments commonly provide incident summaries that allow scientists to target high-value evidence, or those items most likely to reveal the guilt or innocence of a defendant, also known as probative value.

Although the inquisitiveness of laboratory staff sometimes frustrates police officers and prosecutors who are burdened with heavy caseloads, it is this attention to detail that makes our laboratories such powerful entities in our criminal justice system.

Ideally, almost every request of a laboratory will be completed.  In a criminal justice community with professionals having a high degree of expertise in managing and evaluating forensic evidence, this is achievable.  But in an environment where little discretion or professional judgment are exercised to identifying physical evidence most suitable for submission to a forensic laboratory, no amount of laboratory resources or staffing can compensate for the problems that will arise. 

Recommended Reading

Forensic Sciences: Review of Status and Needs

Report to the Attorney General on Delays in Forensic DNA Analysis



Who determines what evidence should be tested by a laboratory?
The overwhelming majority of contemporary literature sources on this subject are clear: Collaboration, expertise, and professional discretion are critical to managing forensic evidence and making decisions about what should be subjected to laboratory testing.  These are not decisions that can be made unilaterally by any one entity; although laboratories must conserve resources in order to remain responsive to the needs of the entire justice community.  Every criminal justice professional having a sound understanding of forensic evidence and a basic respect for the finite resources of forensic laboratories must be allowed to contribute to these decisions.

Recommended Reading

Early Case Evaluation by a Multidisciplinary Team

DNA Evidence: What Every Law Enforcement Officer Should Know



Evidence Triage - is this something new?
No it isn't.  It has always been understood that police officers must be aggressive in collecting crime scene evidence that may have the potential to reveal the truth about a crime and the person(s) responsible for committing it.  Because today's forensic laboratories are so complex and so busy, scientists cannot travel to crime scenes as they once did.  For this reason, police agencies employ and train personnel to respond to crime scenes, identify critical evidence, and preserve the integrity of evidence for use in court.  

Once physical evidence is collected and transported to a police property room, decisions must be made about what items of physical evidence may hold the clues necessary to solve the crime and prosecute the person(s) responsible.  Some of these clues can only be revealed using the methods and instruments of a forensic laboratory.

For these decisions to be made properly, police investigators initiate a process of reviewing the circumstances surrounding the crime.  This may include speaking with witnesses, interviewing doctors that treated the victim, and evaluating the investigative work performed at the scene.  The process also involves identifying the items of physical evidence requiring laboratory testing.  An experienced and well-trained investigator knows that by focusing on high-value evidence, he or she more likely to get faster results, and is less likely to overload the laboratory, which causes delays in many other cases that are important to the investigator.    

This process of evaluating the relationships between items of physical evidence and the circumstances of a crime, followed by the determination of what items must be immediately transported to the forensic laboratory, is commonly referred to as evidence triage, or Front End Forensics.  The use of the term triage is somewhat new in describing this process, but the process itself is as old and common as forensic science itself.

Recommended Reading

The Role and Impact of Forensic Evidence in the Criminal Justice Process (2010)

Survey of Law Enforcement Forensic Evidence Processing (2007)

DNA Policy Considerations for the Prosecutor (See Introduction, Page 2)


Police officers and scientists are not trial lawyers.  It is the prosecutors who carry the burden of proof and therefore determine what evidence is probative or not.
There is no question that prosecutors have enormous responsibility, including the determination of what evidence is likely to prove the elements of a crime for which a defendant has been charged.  The legal value of evidence, however, can be unintentionally mis characterized if the scientific value is not fully understood.  For this reason, the professional judgment of forensic scientists may sometimes put them at odds with prosecutors.  For example, laboratory personnel may determine that a requested analysis has no potential to produce scientific answers to a legal question, or that the nature of the evidence is likely to cause confusion that will mislead a judge or jury.

This is a common problem, for example, with gunshot residue analysis, which involves swabbing the hands of subjects to determine if they fired a gun.  The absence of residue, unfortunately, does not prove that the subject did not fire a gun.  Similarly, the presence of residue does not mean that the subject did fire a gun.  Prosecutors may argue that simply knowing the answer, one way or the other, has value and that it should be left up to a judge or jury to decide.  The fact is, however, that scientists have a responsibility to defendants, the judges, and the juries as well.  Scientists therefore deserve heavy criticism when they knowingly produce scientific results that are confusing.  As a result, laboratories try to conserve precious resources by not performing work that is unlikely to have value, or that is likely to cause confusion about the defendant's guilt or innocence.

Recommended Reading

Policy Considerations for the Prosecutor

Strengthening Forensic Science in the United States: A Path Forward (2009)

Does Contextual Information Affect Expert Opinions?


Lawyers are not scientists.  How do they know what tests should be conducted?
Just as forensic scientists have education and training that allow them to make decisions having legal significance, trial lawyers have enough understanding of expert witnesses to know what a forensic laboratory should be doing in a particular case.  Conflicts do arise from time to time but are rarely so serious that some agreement cannot  be There is some truth to this way of thinking when forensic common ground cannot be found.  

Interestingly, high laboratory backlogs tend to result in more frequent interactions between scientists and prosecutors. High forensic laboratory backlogs significantly lengthens the time it takes a laboratory to produce its results.  Consequently, many cases are brought before a judge or jury before the laboratory has even begun its work.  This creates a situation where prosecutors are required to consult more frequently with scientists to prepare for a trial or other proceeding.  As a result, the inherent differences between science and law have more opportunities to conflict.

The best policy for the criminal justice system is to end forensic laboratory backlogs as quickly as possible and prevent them from ever returning.  

Recommended Reading

Use of Forensic Evidence by Police and Courts (1987)

The Evolution of Forensic Science: Progress Amid the Pitfalls (2007)


Thanks to shows like CSI, juries expect every piece of evidence to be tested.  When it isn't, they assume that the system failed.
The education or instruction of juries is part of normal business in a courtroom.  If a jury is not properly informed to understand why the absence of forensic testing is not indicative of professional malpractice, then the same jury may be at equal risk for believing that the presence of forensic testing is proof of guilt when, in fact, it was not.  This phenomenon has repeatedly been exposed in convictions that were later overturned.

Educating juries about the value and limitations of forensic evidence has never been more important.  Particularly with the sensitivity of DNA and latent fingerprint testing in today's forensic laboratory, a misinformed jury can place an innocent defendant at risk, or cause overwhelming evidence of guilt to be undervalued.  

Recommended Reading

The CSI Effect: Does it Really Exist?

Can Jury Trial Innovations Improve Juror Understanding of DNA Evidence?

Rules of Evidence on Expert Testimony (Federal and States)

Focus Group on Scientific and Forensic Evidence in the Courtroom


Scientists are sometimes unavailable due to illness or retirement.
Our laboratories frequently retest evidence when a scientist is unavailable for court.  The major problem, however, is that testing of evidence involves consumption, which can complicate matters at a later time if additional testing is needed.

The Michigan State Police Forensic Science Division expects all current and former employees to be fully cooperative when their services are needed after leaving our division.  Prosecutors and defenders should cooperate to minimize the personal impact of a court appearance, but should never tolerate an expert witness who is uncooperative or who quotes an inappropriate fee to appear in court.