Phys­i­cal and foren­sic evi­dence, if prop­erly pre­served, col­lected, main­tained, ana­lyzed and reported often is the unim­peach­able source of the truth.  Know­ing this we also explored the the­ory of the Locard Exchange Prin­ci­ple and how “every con­tact leaves a trace” which leads us nat­u­rally to the need to prop­erly secure the crime scene to avoid alter­ing it and con­t­a­m­i­nat­ing the con­tents of the scene.

One of the meth­ods for crime scene inves­ti­ga­tion, pro­cess­ing and devel­op­ment that we vis­ited last week was the Carte­sian or Rec­tan­gu­lar Coör­di­nate Sys­tem.

The next most pop­u­lar method and the one most typ­i­cally used in wide open spaces with­out clear cut bound­aries is the Polar Coör­di­nate System.

Above pic­tured is a sim­ple exam­ple of a Polar Coör­di­nate Sys­tem grid where every red mark indi­cates a uni­form inter­val from the pole

It is a math­e­mat­i­cal process whereby we have a cen­tral point that is called the pole.  From this cen­tral point or pole, we plot out places of inter­est which are cal­cu­lated in terms of dis­tance from the pole as well as the angle from the pole in a fixed direc­tion.  This way after the scene is released we have data that is trace­able and can be used later to deter­mine where var­i­ous objects or evi­dence were rel­a­tive to one another.

Above pic­tured is a Planime­ter that helps to make a proper Polar Coör­di­nate Sys­tem model

If we don’t have a math­e­mat­i­cal and log­i­cal process of pre­serv­ing, record­ing and devel­op­ing a crime scene, then we are reduced to being the func­tional equiv­a­lent of the inter­ested tourist who tramps about and for­ever alters a scene and con­t­a­m­i­nates it for­ever due to the Locard Exchange Principle.

“Look honey, isn’t that neat? Some blood over there” says the crime scene tourists step­ping on top of the shoe prints lead­ing up to the blood

“I’m all ready to look for cool stuff at the scene and what­ever inter­ests me” says the crime scene tourist

“Wow! Lookie here! A bul­let hole in the far away wall. I’m going to walk across the car­pet to get a quick photo of it for the fam­ily album (while I track trace evi­dence from out­side across the scene)” says the crime scene tourist