Cont­a­m­i­na­tion of a crime scene is the enemy of truth.

We have to be aware of crime scene contamination

Every­one rec­og­nizes that the enemy of crime scene inves­ti­ga­tion is con­t­a­m­i­na­tion and the alter­ing of impor­tant phys­i­cal evidence.

The fed­eral gov­ern­ment in the United States Depart­ment of Jus­tice, Office of Jus­tice Pro­grams, National Insti­tutes of Jus­tice,  and specif­i­cally the Tech­ni­cal Work­ing Group on Crime Scene Inves­ti­ga­tion (TWGCSI) spent years of study and inves­ti­ga­tion in the late 1990s which resulted in the pub­lish­ing of guide­lines for crime scene inves­ti­ga­tion that rec­og­nize this salient and hope­fully obvi­ous fact.  The year 2000 pub­li­ca­tion is enti­tled, “Crime Scene Inves­ti­ga­tion:  A Guide for Law Enforce­ment”.  This text is a use­ful frame­work and intro­duc­tion into the prin­ci­ples and pro­ce­dures in terms of best prac­tices as to pre­serve and col­lect a crime scene to avoid alter­ing or contamination.

A decade has passed.  How has local and state law enforce­ment reacted?

Every police depart­ment should have a well-published and well-known and prac­ticed Stan­dard Oper­at­ing Pro­ce­dure (SOPs) in terms of the proper secur­ing of a crime scene.

Does this happen?

At least around where I am in Cen­tral Penn­syl­va­nia, police depart­ments gen­er­ally do not main­tain SOPs as to crime scenes.

Post­ing a sen­try at a crime scene is a good first step

The steps that should be uni­formly present in a well devel­oped SOP as to crime scene preser­va­tion include the following:

1. An acknowl­edg­ment and edu­ca­tion to first respon­ders of the need to be aware of phys­i­cal and foren­sic evi­dence and how the the­ory of the Locard Exchange Prin­ci­ple plays into the crime scene;
2. An acknowl­edg­ment that when one is called to a crime scene that the ulti­mate con­clu­sions or prob­a­bil­i­ties to explain the occur­rence is not known and as such one should not walk in with a cog­ni­tive bias but rather with the idea that every­thing may later prove to be sig­nif­i­cant and hence the need secure and pre­serve the scene in its orig­i­nal state so as to doc­u­ment and cat­a­log in a mea­sur­able and mean­ing­ful way so that oth­ers who later review the notes, pho­tos and doc­u­ments who were not on the scene can use the data gen­er­ated in that is it both accu­rate and pre­cise.  This should be the goal;
3. A recog­ni­tion that the order of pro­cess­ing a scene is impor­tant, just as the order of pre­serv­ing the scene is impor­tant (e.g., the set­ting up of a crime scene perime­ter, but also in the fash­ion of fin­ger­prints in blood spat­ter first then blood spat­ter or blood spat­ter first then fingerprints);
4. The under­stand­ing that some evi­dence may very well be tran­si­tory in nature such as volatile organic compounds;
5. The need to imme­di­ately secure the scene as soon as possible;
6. The need to secure and con­trol per­sons at the scene and the acknowl­edg­ment that those at the scene who may not even be involved may them­selves con­tain mean­ing­ful evi­dence on their per­son such as blood or par­ti­cles such as gun­shot residue;
7. Doc­u­ment, doc­u­ment and then again document

With­out preser­va­tion we are reduced to being tourists at a crime scene

With­out a well-promulgated, well-defined, well-entrenched and uni­ver­sally imple­mented SOP for crime scene preser­va­tion, then even the best col­lec­tion and analy­sis later will be jus­ti­fi­ably ques­tioned as a large mis­take was made in the begin­ning.  The old phrase garbage-in leads to garbage-out comes to mind.  With­out a well-preserved crime scene, we are reduced to being tourists gawk­ing and tramp­ing through the crime scene for­ever chang­ing and alter­ing it.