Introduction to CSI

On TV police dramas and movies, viewers get to watch as investigators find and collect evidence at the scene of a crime. Crime show characters can make blood appear as if by magic and piece together seemingly unrelated clues to solve crime. Many of us believe we have a pretty good grip on the process. But does Hollywood get it right? Do crime scene investigators follow their DNA samples into the lab? Do they interview suspects and catch the bad guys, or is their job all about collecting physical evidence? What really goes on when a CSI "processes a crime scene"? Let’s find out.

Crime scene investigation is the meeting point of science, logic and law. "Processing a crime scene" is a long, tedious process. It involves careful consideration and documentation of the conditions at the crime scene. It also involves collecting any physical evidence that could possibly explain what happened and point to who did it. There is no typical crime scene. There is no typical body of evidence or set of clues. And there is no typical investigative approach.

At any given crime scene, a CSI might collect dried blood from a windowpane -- without letting her arm brush the glass in case there are any latent fingerprints there. Or she might lift hair off a victim's jacket using tweezers so she doesn't disturb the fabric enough to shake off some odd-coloured dust in the folds of the sleeve. All the while, the physical evidence itself is only part of the equation.

The ultimate goal is the conviction of the person behind the crime. So while the CSI is poking, prodding, scraping and scouring through stuff without disturbing any trace evidence, she's also considering all of the necessary steps to preserve that evidence. She’s also thinking about what the lab can do with this evidence in order to reconstruct the crime or identify the criminal. And the entire time she’s doing her job, she has to keep in mind any legal issues involved in making sure this evidence is admissible in court.

Who's at the Scene?

Many people performing a variety of jobs will be on hand at a crime scene, including the following:

Police officers are typically the first to arrive at a crime scene. They arrest the perpetrator is he's still there and call for an ambulance if necessary. They are responsible for securing the scene so no evidence is destroyed.
The CSI unit documents the crime scene in detail and collects any physical evidence.
The district attorney is often present to help determine if the investigators require any search warrants to proceed and obtain those warrants from a judge.
Specialists (entomologists, forensic scientists and forensic psychologists) may be called in if the evidence requires expert analysis.
Detectives interview witnesses and consult with the CSI unit. They investigate the crime by following leads provided by witnesses and physical evidence.

The investigation of a crime scene begins when the CSI unit receives a call from the police officers or detectives on the scene. The overall system works something like this:
The CSI arrives on the scene and makes sure it is secure. Securing the crime scene -- and any other areas that might later turn out to be part of the crime scene -- is crucial. A CSI really only gets one chance to perform a thorough, untainted search -- furniture will be moved, rain will wash away evidence, detectives will touch things in subsequent searches, and evidence will be corrupted. Securing the scene involves creating a physical barrier using crime scene tape or other obstacles like police officers, police cars or sawhorses. It’s also important to remove all unnecessary personnel from the scene. A CSI might establish a "safe area" just beyond the crime scene where investigators can rest and discuss issues without worrying about destroying evidence.

Details

While searching the scene, a CSI is looking for details including:
Are the doors and windows locked or unlocked? Open or shut? Are there signs of forced entry, such as tool marks or broken locks?
Is the house in good order? If not, does it look like there was a struggle or is the homeowner just messy?
Is there mail lying around? Has it been opened?
Is the kitchen in good order? Is there any partially eaten food? Is the table set? If so, for how many people?
Are there signs of a party, such as empty glasses or bottles or full ashtrays?
If there are full ashtrays, what brands of cigarettes are present? Are there any lipstick or teeth marks on the butts?
Is there anything that seems out of place? Maybe there's a glass with lipstick marks in a man's apartment, or the toilet seat's up in a woman's apartment. Is there a couch blocking a doorway?
Is there trash in the trashcans? Is there anything out of the ordinary in the trash? Is the trash in the right chronological order according to dates on mail and other papers? If not, someone might have been looking for something in the trash.

Once the crime scene is secured, the next step is to get the district lawyer involved. This is a must -- if anyone could possibly have an expectation of privacy in any portion of the crime scene, the CSI needs search warrants. The evidence a CSI recovers is of little value if it's not admissible in court. A good CSI errs on the side of caution and seldom searches a scene without a warrant.

She does an initial walk-through to get an overall feel for the crime scene, finds out if anyone moved anything before she arrived, and generates initial theories based on visual examination. She makes note of potential evidence. At this point, she touches nothing – she is only using her eyes, ears, nose, some paper and a pen. Crime scenes are three-dimensional. CSIs should remember to look up. Also, if a CSI shines a flashlight on the ground at various angles, even when there's plenty of lighting, she'll create new shadows that could reveal evidence.

Next, the CSI thoroughly documents the scene. The goal is to create a visual record that will allow the forensics lab and the prosecuting attorney to recreate an accurate view of the scene. The CSI uses digital and film cameras, different types of film, various lenses, flashes, filters, a tripod, a sketchpad, graph paper, pens and pencils, measuring tape, rulers and a notepad at this stage of the investigation. In crime scene investigation, opinions don't matter and assumptions are harmful. When describing a crime scene, a CSI makes factual observations without drawing any conclusions. She documents the scene as a whole and documents anything she has identified as evidence. She still touches nothing.

Collecting Evidence

After the CSI has created a full record of the crime scene exactly as it was when she arrived, it's time to collect the evidence. Now it's time to touch stuff -- very, very carefully. The CSI systematically makes her way through the scene collecting all potential evidence, tagging it, logging it and packaging it so it remains intact on its way to the lab. Depending on the task breakdown of the CSI unit she works for and her areas of expertise, she may or may not analyze the evidence in the lab.

Every CSI unit handles the division between field work and lab work differently. What goes on at the crime scene is called crime scene investigation (or crime scene analysis), and what goes on in the laboratory is called forensic science. Not all CSIs are forensic scientists. Some CSIs only work in the field -- they collect the evidence and then pass it to the forensics lab. In this case, the CSI still needs to understand the basics of forensic science. This way she can recognize the specific value of various types of evidence in the field.

Specialty Departments within a Crime LabCrime labs can include several special departments. Often, a piece of evidence passes through more than one department for analysis. Here are a few examples of specialty departments:
Latent fingerprints and impressions -- Develop latent fingerprints; analyze and compare fingerprints, footwear and tire impressions; run fingerprints through the Automated Fingerprint Identification System (AFIS, which utilizes the FBI database) for comparison against hundreds of millions of prints
Chemistry -- Conduct analysis and comparison of illicit unknown chemicals and other materials
Computer Crimes -- Recover evidence from computers; perform computer enhancement on audio or video evidence
Firearms and toolmark identification -- Identify firearms; test firearms to establish barrel pattern and distance of gun from entrance wound; identify and compare bullets, casings and toolmark impressions
Serology and DNA -- Conduct body fluid analysis, including DNA analysis for blood stains, semen and hair for identification and comparison

The crime lab processes all of the evidence the CSI collects at the crime scene. When the lab results are in, they go to the lead detective on the case.

As we mentioned earlier, the CSI has several main goals in mind when collecting evidence from a crime scene: Reconstruct the crime, identify the person who did it, preserve the evidence for analysis and collect it in a way that will make it stand up in court. Evidence can come in any form.

Body of Evidence

Blood found at a crime scene can tell investigators a whole lot of things. Samples can be taken from clothing, furniture or other surfaces. For example, if there is dried blood on any furniture at the scene, the CSI will try to send the entire piece of furniture to the lab. A couch is not an uncommon piece of evidence to collect. If the blood is on something that can't reasonably go to the lab, like a wall or a bathtub, the CSI can collect a sample of the blood by scraping it into a sterile container using a scalpel. The CSI may also use luminol and a portable UV light to reveal blood that has been washed off a surface. The lab will perform DNA analysis of any submitted sample so it can be used later to compare to blood taken from a suspect. If there’s blood at the scene, there may also be blood spatter patterns. Spatter patterns can happen during a scuffle or fight. These patterns can reveal the type of weapon that was used during the scuffle. Analyzing a blood pattern involves studying the size and shape of the stain, the shape and size of the blood droplets and the concentration of the droplets within the pattern. The CSI takes pictures of the pattern and may call in a blood-spatter specialist to analyze it.

With theories of the crime in mind, CSIs begin the systematic search for incriminating evidence, taking meticulous notes along the way.

The actual collection of physical evidence is a slow process. Each time the CSI collects an item, she must immediately preserve it, tag it and log it for the crime scene record. Different types of evidence may be collected either at the scene or in the lab depending on conditions and resources, such as:

Trace evidence (paint residue, broken glass and unknown chemicals) - To collect trace evidence, a CSI might use tweezers, plastic containers with lids, a filtered vacuum device, a knife and a biohazard kit (which contains disposable latex gloves, booties, facemask and gown and a biohazard waste bag). Trace evidence is important.
Impressions (fingerprints, footwear, tool marks) - Tools for recovering fingerprints include brushes, powders, tape, chemicals, lift cards, a magnifying glass and Super Glue. For three-dimensional impressions, like a footprint, a CSI will use a casting kit. A casting kit might include multiple casting compounds (dental gypsum, Silicone rubber), snow wax (for making a cast in snow), a bowl, a spatula and cardboard boxes to hold the casts. For toolmark impressions, a cast is much harder to use for comparison than it is with footwear. If it's not feasible to transport the entire item containing the tool mark, a CSI can make a silicone-rubber cast and hope for the best. Body fluids - To identify and collect these pieces of evidence, a CSI might use smear slides, a scalpel, tweezers, scissors, sterile cloth squares, a UV light, protective eyewear and luminol. He'll also use a blood collection kit to get samples from any suspects or from a living victim to use for comparison.
Hair and fibers - A CSI may use combs, tweezers, containers and a filtered vacuum device to collect any hair or fibers at the scene.
Questioned documents (diaries, notes, phone books; also includes electronic documents like answering machines, cell phones, PDAs and caller ID units) A documents lab can often reconstruct a destroyed document, even one that has been burned, as well as determine if a document has been altered. Technicians analyze documents for forgery, determine handwriting matches to the victim and suspects, and identify what type of machine was used to produce the document.

Remember, all this time and effort is necessary – it could be the difference between a crime going unsolved or the police catching the culprit

Examining the Scene

There are several search patterns available for a CSI to choose from to assure complete coverage and the most efficient use of resources. These patterns may include:
The inward spiral search: The CSI starts at the perimeter of the scene and works toward the center. Spiral patterns are a good method to use when there is only one CSI at the scene.
The outward spiral search: The CSI starts at the center of scene (or at the body) and works outward.
The parallel search: All of the members of the CSI team form a line. They walk in a straight line, at the same speed, from one end of crime scene to the other.
The grid search: A grid search is simply two parallel searches, offset by 90 degrees, performed one after the other.
The zone search: In a zone search, the CSI in charge divides the crime scene into sectors, and each team member takes one sector. Team members may then switch sectors and search again to ensure complete coverage.

This is a great website with lots of stuff about CSI. It called it FBI because its American but its still good!

http://www.fbi.gov/kids/k5th/whatwedo3.htm