drops of blood

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If you're flipping channels one day and come upon a crime scene as depicted on ­one of the many TV shows that focus on forensic science -- like "CSI" or "Dexter" -- you may have noticed something that seems pretty unusual. Amongst the technicians dusting for fingerprints and collecting hair fibers at the murder scene, the camera pans on an array of red strings running from the floor, the wall, the table and the sofa. All of the strings seem to meet in a specific area.

­Suddenly, an investigator begins recounting aspects of the crime, like when it happened, where the assault took place in the room, what kind of weapon was used on the victim and how close the assailant was to him. How could he have learned that information from strings?

­The strings themselves aren't important. They're simply a tool to help investigators and analysts draw conclusions about a substance that's often found at crime scenes: blood. We've become used to hearing how blood samples are used to identify someone through DNA. But the blood itself -- where it lands, how it lands, its consistency an­d the size and shape of the blood droplets, or spatter -- can determine a lot of significant aspects of the crime.

Of course, analyzing blood splatter isn't nearly as simple as fictional bloodstain pattern analysts like Dexter Morgan might make it appear to be. Experts in the field often say that it's as much an art as it is a science. If there happen to be multiple victims and multiple assailants, it becomes even more complex. But a well-trained and seasoned bloodstain pattern analyst can often provide key information that leads to arrest and conviction.

Let's start with the basics of bloodstain pattern analysis -- for example, what blood spatters can reveal (and what they can't).