Processing the Interior of the Scene
Inexperienced investigators often neglect to process the inside of the offender entry point — the inside of the broken or cut fence, and the inside of the door or window where the intruder entered. This is every bit as important as is the exterior, and may provide evidence not found in any other place. For instance, the intruder could've cut himself on raw edges of the fence, leaving behind blood and possibly clothing.
When entering the residence or building, be careful where you step and place your hands. Evidence is everywhere, and although you're wearing disposable gloves, you can easily disturb an important sample. Evidence isn't only important for itself, but for where it has been found.
When inside, examine pry or tool marks from the inside, cast and photograph them. Look for latent prints on areas next to point of entry and process any found. Latent prints are the result of organic and inorganic substances as well as environmental ones. When water in perspiration evaporates, these substances are deposited on surfaces touched in the pattern of each person's unique fingerprints. Substances that lead to the deposit of latent prints are:
Organic substances — byproducts of food metabolism such as fats, oils and waxes contained in perspiration
Organic substances — certain vitamins in perspiration allow for laser identification of prints
Inorganic compound — salt in perspiration
Environmental substances — matter picked up during contact with the environment, specifically plant pollen, grease, oils, dust, soot, animal hair and dander, insect material, human hair and body preparations and treatments
Environmental substances — dust and foreign matter from the crime scene itself
Experienced detectives realize that fingerprints are often unavailable at a crime scene, and that what is most often available are partial prints. Still, they must search for prints, in case even one is present. Partial prints have been used, successfully, to match offenders to a weapon or crime. Yet it's definitely more difficult to match using partials than when making comparisons using a whole or entire print. By the way, unless you've been trained in lifting prints or collecting evidence, don't attempt to do it yourself. Hire a professional to walk through the scene with you and perform the tasks you can't.
The knowledgeable detective also realizes that even when prints are deposited, they're very often blurred or smudged beyond possibility of identification. He knows that it's possible to handle a weapon or an object with bare hands and never leave any prints at all — it's rare, but possible. So, a defense attorney's warning to the jury that “if there are no prints you must not convict” simply won't hold water. Other factors influencing whether prints are deposited on surfaces follow:
Some people don't sweat sufficiently to leave prints
The sweat of certain people doesn't produce enough necessary organic substances for prints to remain
The nature of the surface touched, whether porous or smooth, affects whether prints remain
Temperature, humidity and other environmental factors contribute a good bit
The manner in which the surface was touched may have caused smudged prints
After processing the inside of the entry point, continue your search for evidence by moving through the house along the path which the offender appears to have taken. Watch the floor and walls for evidence, and the ceiling as well. If the crime was egregiously violent, evidence could be anywhere, including above you. The admonition to look up is not only to help you locate evidence, but is given for your protection from blood or body fluids which may drip from the ceiling or from lamps. This is one reason for protective clothing and goggles.
As you move through the scene, if shoeprints are visible, photograph them. You might use a crime lamp to identify faint prints, holding the light at an angle in order to illuminate foot or hand prints. If you spot one of these, a shoeprint residue lifter with adhesive on one side will lift the print pattern nicely. This pattern can be used, later, to compare with a suspect's shoe print. While there are other methods for lifting shoeprints, this is a very common and fairly inexpensive one.
Check doors and drawers the offender may have opened. If a large amount of blood contaminates the floor and areas you must touch, beware of splash back — tiny droplets of blood or fluids which splash when disturbed, and deposit on your shoes, clothes or person. To guard against this, forensic techs often wear goggles, facial coverings, aprons and blood boots: clear boot-shaped plastic coverings that protect from body fluids which may contain disease.
A forensic investigator, in a department with available funds for expensive tools, will often wear a full body suit protecting her from dangerous evidence, and protecting the scene from her own trace evidence of hair, fibers, perspiration, and blood should she be injured. In this scenario, you're wearing one too.
When reaching the body or area where the body has been, photograph the spot from all angles. It's important to keep at least one item from the previous photo in the subsequent one in order to provide perspective. For instance, if a cat bed sits at the right edge of one photo, include that bed in the left edge of the next photo, then continue around the room in the same manner, and back to the first photo.
When it's fresh, blood evidence is usually obvious, but exposure to air, sunlight, bacteria, heat, and age can alter it so much that it's difficult to recognize. Many field (presumptive) tests exist which disclose the slightest residue of blood evidence. One of these tests is performed with luminol. Luminol is only used as a last resort, however, especially if the suspected blood material is very limited. One reason is that in some cases, these types of tests can render the results of the “precipitin test” inconclusive. The precipitin test determines whether blood is from an animal, human. This test is also important because, performed on a sample that's been well-preserved and is of sufficient quantity, it can provide blood type as well.
These field tests aren't usually admissible into evidence, but they have extensive investigative value. For instance, if your field test uncovers the crime scene or scenes, the field test is worth its weight in gold, as processing of the scene can begin. DNA tests are best done in a lab, using sophisticated equipment.
You may investigate a scene where an attempt has been made to clean up evidence, as many criminals are under the mistaken impression that blood can be removed with soap, Clorox or some other chemical. The scene may look spotless. In this case, how do you know where blood may have been deposited? Field tests will alert you when blood is present once you've isolated a suspicious spot. So how can you locate the area you need to test? The following list will familiarize you with examples of suspicious areas:
A bedspread, mattress or piece of furniture is missing — the reason for its absence cannot be adequately explained, nor its whereabouts confirmed
There's a spotlessly clean floor or area in an otherwise dirty and unkempt home or building — or in a relatively clean home, a much cleaner, newer, area jumps out at you
Carpet or flooring that has been recently replaced, or part of the carpet or floor boards look different, newer than that of the surrounding area, and are without use and age marks of that area
Seat cushions have been removed, from chairs, couches or vehicles, and/or replaced
Pieces of a set of furniture or a vehicle's seat covers have been freshly recovered
Furniture or rug has been moved to an inappropriate or inconvenient area, leaving a lighter spot where it seems to have been more appropriately placed — it may be covering a stain
The area has been recently painted, or the paint is limited to one or several walls, instead of all
Some other substance appears to have been rubbed into carpet or floor material in an attempt to create a new stain to mask a blood stain
Next, make a sketch of the floor plan, the perimeter and everything in the room. This sketch is intended to include all furniture and items where they sit. It must show windows and doors, and whether doors open to the inside or outside. It must be very detailed. Many software programs are available for this purpose and some departments employ, as a special part of the forensic team, a computer crime scene reconstruction officer.
The next step is to take measurements. Indicate the distance of objects in relation to each other, and in relation to other items in the room. When moving through the crime scene, always collect any large evidence first — soda or beer cans, wine bottles and glasses, anything that may have been touched.