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¶ … scientific method refers to a way of investigation or the acquisition of knowledge through the testing of a theory or hypothesis, then working through measurements (observation and empirical notes) to come up with a result, which should prove or disprove the original theory. Thus, the basic method consists of a) formulating a question or hypothesis, b) designing an experiment or means of collecting data, c) observation or experimentation, d) analyzing the results and considering the proof or disproof of the hypotheses, and e) suggestions for future research (Cary, 2003). The purpose of this lab was to observe reactions of various presumptive blood testing kits on suspected stains in order to assess if the stains have a positive, negative, or a false-positive reaction.
Methodology -- Using Phenolpthalein (KM) presumptive kit and known bloodstain cards for comparison, swabbed samples were compared with certain stains. Color changes were observed. The areas next to the stain were also swabbed and the resulted compared to known agents using Leucocrystal Violent (LCV). Once positive control test is completed, steps are repeated to conduct the actual presumptive test. Negative control is similarly established . Tetramethylbenzidine (TMB) is used as the positive control. Care should be taken to prevent contamination, duplication of tests should be conducted to verify reactive results.
Material Samples -- for the test, samples were used that could have the outward appearance of being blood and, by their color, containing hemoglobin. These included: Red Paint, Smashed Potato, Cooked Tomato Sauce, Red Food Coloring, Fresh Raw Beet, Actual Blood from test kit.
Results: The results for this test are presented in the table below:
Table 1 -- Sample Test Reactions
Substance
KM
LCV
TMB
Result
Misc.
Red Paint
N
N
N
Not Blood
Potato
N
N
N
Not Blood
Cooked Tomato Sauce
FP
FP
FP
Not Blood
FP required retests
Red Food Coloring
N
N
N
Not Blood
Fresh, Raw Beef
FP
FP
FP
Blood Elements
FP required retests
Blood Sample
Pink
Purple
Green
Blood Present
REFERENCES
Cary, S. (2003). A Beginner's Guide to the Scientific Method. Wadsworth.
Schiro, G. (2011). "Collection and Preservation of Blood Evidence from Crime Scenes." Crime Scene Investigator Network. Cited in:
http://www.crime-scene-investigator.net/blood.html
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