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Blood patterns
In This Section


     All patterns of the blood are dependent on the surface that they hit.  The texture changes how a drop of blood lands on a surface.  With this in mind, all comparisons on splatter must occur on identical surfaces.

     A drop of blood first tells the direction it was traveling.  If you look carefully at a drop of blood, the pointed end will show the direction it was moving towards.  Cast off in the form of droplets will spread ahead of the main drop.

     Blood Splatter tells the impact angle of the blow.  The lesser the angle, the greater the drop is rounded.  To find the impact angle, you need to use some math.  The formula is as follows:

Width of the spot / length of the spot = the impact angle as a function of sine

Example:  a spot is 3 mm wide and 11 mm long.

3 / 11 = .273 fn of sine = 15.8 degrees

Play with your calculator to see how to get this answer.  Each calculator is different.  If you can't figure out how to use sine (or don't have a scientific calculator) just write .273 fn of sine  This still tells me you understand what to do.

     Finally, despite what anyone else tells you, size does matter.  The larger the drop, the less "stress" related to getting the splatter.

Large drops (ones greater than 6 mm) are typically due to dripping.  When you give yourself a deep paper cut, blood drips straight down.  This leaves larger pools rather than splashes.  Moving slowly to get a band-aid allows some narrowing of the front end of the drop but with so much liquid in each drop, the splatter remains large and circular.

Medium drops range from 2 mm to 6 mm.  These drops typically are due to a victim being beaten.  There is more force behind the cast off, causing smaller drops.  The cast off tends to be two or more directions as well.

Fine drops that range from 0.1 mm to 2 mm are caused by violent or high energy actions.  This type of drop is typical of coughing up blood.  The force sprays fine particles of blood in a fanning pattern.

Mist are drops that are less than 0.1 mm.  This indicates high-velocity trauma.  Typical sources are high powered rifles or close contact firearms.  Mist may even occur on a suspect because of the proximity to the initial impact.

     The point of origin of the blood splatter is determined by drawing straight lines through the long axis of several splatters.  The point where all the lines meet is called the point of convergence and represents the place of origin.  This is the dramatic laser line ups and strings layered across the crime scenes that you see on TV.  Because it is so visual, it helps to set up the reconstruction.  The point of origin can indicate the height and positions of suspect and victim.  It can distinguish areas that should have blood and don't (voids); it also can tell the order that events likely happened.  Good reconstruction has led to murder convictions.  The suspect doesn't believe that the reconstruction could have occurred without a camera present and so believes that they are caught on tape.  They confess in the hopes of getting a better sentence.