drops of blood

What can some little drops of blood tell us about a crime?

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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, such as "CSI" or "Dexter," you might notice something strange. Among the technicians dusting for fingerprints and collecting hair fibers at the murder scene, you spot an array of red strings running from the floor, the wall, the table and the sofa. All of the strings meet at nearly the same point.

Suddenly, an investigator begins recounting aspects of the crime: When it happened, where the assault took place in the room, what kind of weapon the perpetrator used and how close to the victim the assailant stood. How could he have learned all that information from a webwork of strings?

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

Of course, analyzing blood spatter isn't as simple as fictional bloodstain pattern analysts like Dexter Morgan make it appear. Experts in the field often say that it's as much an art as a science. Although important aspects of bloodstain pattern analysis are well supported by research, analysts must be careful not to overreach [source: Iowa State]. If the violent act involves multiple victims and multiple assailants, the challenge becomes even more complex. But a well-trained and seasoned analyst can 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).