back

CASE FILE

Police are called to a hotel ballroom where they discover a semi-conscious woman on the floor. After a brief investigation of the scene, the woman went into a coma. There is a fresh pool of blood by the victim’s head. Officers question the hotel staff and learn that the woman’s fiancée and maid-of-honor, her sister, were helping her decorate the room for her wedding reception just hours before. They were able to find the fiancée and maid-of-honor staying in their respective hotel rooms. During a voluntary search of both hotel rooms, they recover a pair of linen pants with dark stains from the closet of the fiancée and a shawl with similar dark stains from the maid-of-honor.

Your forensics lab arrives at the scene:

Please write a detailed description of the scene.

Your forensics lab receives the following items to test:

Sample 1: Stained cloth from the fiancée’s pants

Sample 2: Stained cloth from the maid-of-honor’s shawl

Sample 3: Blood collected from under the victim’s head

First, test the stained cloths to determine if the stains are caused by blood. Place a drop of phenolphthalein/peroxide solution on each stain. A purple-violet color change indicates that blood is present. The absence of the color change indicates that blood is not present. Record your results.

Color reaction for Sample 1:____________________

Color reaction for Sample 2:____________________

Based on the results of this test, which person, the fiancée or the maid-of-honor, becomes your chief suspect?

____________________________

When confronted, your chief suspect claims to have badly cut himself while hanging a disco ball, thus accounting for the bloodstain. Investigators have now been able to recover a blood sample (Sample 4) from the disco ball. It is suitable for blood typing. The suspect voluntarily gives a blood sample (Sample 5). Proceed as follows to type your three blood samples.

1. Using the dropper vial, place a drop of Sample 3 (the victim’s blood) in each well of the blood typing tray. Replace the cap on the dropper vial. Always replace the cap on one vial before opening the next to prevent cross contamination.
2. Add a drop of anti-A serum to the well labeled A. Replace the cap.
3. Add a drop of anti-B serum to the well labeled B. Replace the cap.
4. Add a drop of anti-Rh serum to the well labeled A. Replace the cap.
5. Using a different color mixing stick for each well gently stir the blood and anti-serum drops for 30 seconds. Remember to discard each mixing stick after a single use to avoid contamination of your samples.
6. Carefully examine the thin films of liquid mixture left behind. If a film remains uniform in appearance, there is no agglutination. If the sample appears granular, agglutination has occurred. Determine the blood type of the sample using the data table below. Answer yes or no as to whether agglutination occurred in each sample. A positive agglutination reaction indicates the blood type.
7. Record the results for the first blood sample in the data table.

DATA TABLE

Thoroughly rinse the blood typing slide, then repeat steps 1 through 7 for Samples 4 and 5, recording the results of each test as you go.

Based on your results, did the blood collected from the disco ball come from the suspect? ___________

Could this blood have come from the victim? ___________

back