Maximizing Crime Lab Results
Written by Edward E. Hueske   

Today’s modern crime laboratory is capable of obtaining unprecedented analytical results. The combination of highly trained forensic scientists and sophisticated instrumentation specifically designed for forensic purposes is an unbeatable combination. Gone are the days when instrumentation designed for some other purpose (e.g. industrial applications) had to be modified for forensic analyses.

There is, however, one aspect of the forensic lab/criminal investigative link that frequently results in less than appropriate analyses or findings. The “disconnect” comes when either the submitting agency fails to request the appropriate analyses, fails to appraise the lab of pertinent case details, or fails to collect adequate specimens for testing or control samples. 

Failure to request appropriate analyses
Most crime labs are not looking for something to do; they have plenty of work and are typically dealing with backlogs of work. Thus “If you don’t ask, you don’t get.” In a perfect world, upon reviewing a case submission and the request for analysis, the forensic scientist recognizes that there are additional tests that could be carried out but were not asked for. The analyst then contacts the lead investigator in the case and suggests additional testing. Actually, that can and does happen, but it is typically something that is more common to a smaller agency with an in-house lab. A large state or federal lab seldom has the ability to carry out that sort of direct communication.
Most state and federal crime labs have manuals that they have created to assist user agencies in the proper collection and handling of physical evidence, but they do not always provide insight on what capabilities the lab might have for various types of evidence. Thus, it is up to the submitting agency to understand both the capabilities and limitations of the crime lab they are dealing with. 
One way of handling that is through training. Unfortunately, most police training academies can only devote a few hours to the subject and depend on other means to educate their investigative personnel (e.g. in-service training classes) as to the specifics of forensic capabilities and limitations. When classes are taught by qualified instructors, this is a good way to get the information across.
Case example:
A police department investigated a shooting incident in which the shooter claimed that he had a rifle out and was examining it when he “fumbled” it. Unintentional discharge occurred, resulting in the bullet striking his girlfriend. A dark deposit was noted near the entry wound on the woman’s chest by the emergency room physician, who categorized it as “gunshot residue from the rifle barrel being in contact (i.e. lying against) with the chest”. 
The rifle was submitted to a state crime lab with the request “examine for biologicals”. There was no explanatory information given regarding the specific need to check the muzzle area for DNA from the victim. The crime lab report, when completed, reflected testing of the stock and trigger areas of the rifle only. Without a specific request or explanatory information, the crime lab had no way of knowing the real area of interest was the muzzle area of the barrel.
Failure to provide pertinent details
Most evidence submission forms provided by crime labs have only very limited space for case detail information. That is primarily by lab design in an effort to avoid a long oration that fails to keep the focus on the forensic specifics. Accordingly, agencies often feel that they are required to “keep within the lines”. 
Whenever there is information that could be critical to explaining the potential findings in forensic analyses, the crime lab needs to be advised. If there is insufficient space provided on the evidence submission form, attaching a supplemental sheet that succinctly and clearly outlines the areas of interest/concern is appropriate.
Case example:
A police officer engaged an individual who was carrying an AK-47. The individual allegedly raised the AK-47 toward the officer, and the officer subsequently fired his weapon. A police agency submitted the AK-47 to the laboratory requesting that it be examined for function testing. However, the agency failed to let the lab know that the weapon may have been struck by a round fired by the police officer.
As it turned out, there was an indentation in the forearm of the AK-47 that could only have resulted from the rifle having been raised up toward the officer at the moment when the officer fired. However, that indentation was not discovered until a year later, when a civil suit had been filed and the rifle was examined by an independent expert. Although the officer had been no-billed by the grand jury, the indentation in the AK-47 was exculpatory evidence and should have been available a year earlier.
Failure to collect appropriate samples/controls
Many times at a crime scene, potential evidence is observed with no apparent source (i.e. “foreign specimens”). Clearly these circumstances limit the ability of the scene investigator to collect control samples for comparison to the evidentiary material. Conversely, when there is a source (or sources) of materials that suggest a likelihood of transfer to an as yet undetermined suspect, it is incumbent on the scene investigator to take control samples for possible future lab comparison. Admittedly, one has to be selective in that endeavor. 
The guiding principle for collecting apparent “foreign” materials at a scene is to collect it rather than risk leaving behind valuable evidence. That requires added time in documentation, packaging, and submission—but it is the best policy. With respect to deciding what should be collected in the way of control samples in “no suspect” cases, practicality combined with good logic should guide the investigator. Obviously, experience is a good thing to base selectivity on, since “you can’t take it all.”
Case example:
The female victim of a homicide, the night clerk at a hotel, was found lying in a pool of blood in the breakfast area adjacent to the hotel lobby. Her throat had been cut and her ankles appeared to have ligature marks. A small piece of white cord was lying on the floor nearby. No source for the cord was found in the immediate area. Because of the ligature marks 
and the lack of any similar cord, officers were sent out to scour the hotel for any similar cord.
The guests had been ordered out of their rooms and were assembled out in front of the hotel in the parking lot. Ultimately, one of the officers sent out to search for a source of the cord returned with a piece about 3 feet long that he had taken from one of the guests who had been using it as a leash for his dog.
A search warrant was obtained for his room and bloody clothing and a piece of cord similar to that found near the body were found. A search warrant was then obtained for the man’s residence and a spool of the cord was located in the garage. 
This case illustrates what may be required to obtain necessary control samples. While it does not always work out as well as it did in this example, if no effort is made the end result is quite predictable.
Case example:
Two youths allegedly took a third youth out to a rural area and into a field where they both purportedly shot him to death. The scene investigator had heard that cartridge case locations are unreliable indicators of shooter location under any circumstance. Accordingly, he merely collected the fired cartridge cases without documenting their locations. Later it was determined only 9mm fired cartridge cases were involved. Had their locations been properly documented, the relative positions of the two shooters could likely have been determined, as well as any movement within the scene from the firearms examiner being able to identify which gun fired which cartridge case.
In summary
The crime lab refers to a familiar saying that pretty much covers most of the issues discussed here:
“Garbage in equals garbage out”
The investigator must understand both the capabilities and the limitations of the crime lab very clearly in order to properly document, preserve, and collect evidence at crime scenes. They must provide pertinent case facts and make specific requests for analyses in order to maximize the possible results of forensic analyses. It is the scene investigators’ responsibility to maintain a “reconstruction mentality” that guides them in making the appropriate requests of the lab.
About the Author
Edward E. Hueske has spent 40 years as a practicing forensic scientist, including 23 years with government crime labs in Texas, Oklahoma, and Arizona (retiring in 1996), and 14 years as a full-time faculty member in the department of criminal justice at the University of North Texas (retiring in 2012). He currently consults with prosecution, defense, and police agencies in civil/criminal matters and provides training to police agencies in shooting incident reconstruction. He is the author of Practical Analysis & Reconstruction of Shooting Incidents (CRC Press 2006), Fingerprints & Firearms (Facts on File 2008), and numerous articles published in various forensic journals. He is a fellow of the American Academy of Forensic Science, Emeritus Member of the American Society of Crime Laboratory Directors, Emeritus Member of The Southwestern Association of Forensic Scientists, and Distinguished Member of the Association of Firearm & Tool Mark Examiners.
< Prev   Next >

Item of Interest

The language barrier between English-speaking investigators and Spanish-speaking witnesses is a growing problem. (Updated 28 February 2011)