Mystery: Crime Solving

Name:______Date:______

Directions: Read through the crime scenario and decide which suspect(s) you think might have done it and why.

The Crime Scene

One morning Mr. Eberle got to the school very early, before anyone else arrived. As he walked toward his classroom, he noticed some droplet-sized dark stains near the door. The door to the classroom was open. Mr. Eberle shouted as he looked in and saw a body on the floor beside the lab desk. He immediately called the police, and soon investigators were on the scene. While he waited, he add snaps of the scene to his story from the doorway (being sure not to enter and possibly contaminate any evidence).

Mr. Eberle watched as investigators collected blood samples that he knew would later be tested to help police determine who might have committed the crime. They took the stained carpet near the door, and samples from the victim. One officer came in saying that he had found a bloody knife in the stairwell, which he had put in a plastic bag and then handed over to investigators. Investigators later identified the body as Mr. Kelley; they rounded up four suspects and got blood samples from each of them as well.

The Blood Tests

Investigators brought all the blood samples back to the lab and tested them using the technique you just learned about. Below are the results they saw on their blood typing slides. Fill in the blood types and answer the questions that follow.

Procedure

1. Put 4-5 drops of blood from one of the samples onto the three wells of a CLEAN tray.

2. In the well labeled A, drop some of the Anti-A serum. Mix gently with a CLEAN stick.

3. Wash the stick before continuing.

4. Repeat steps 3 and 4 for B and Rh.

5. Wait a minute, then record the results in the data table.

6. Repeat steps 1-5 for all samples

Data Table

Victim / Suspect 1 / Suspect 2 / Suspect 3 / Weapon / Carpet
Anti-A
Anti-B
Anti-Rh
Blood Type:

Post-Lab Questions

  1. Whose blood matches the blood on the weapon?
  1. Explain what you think might have happened during the progression of the crime that led to these results.
  1. Are there any suspects that you think did not commit the crime? Why not?
  1. Is blood type enough to convict a suspect of murder? Why or why not?
  1. Why does agglutination occur when antibodies are added to the blood?
  1. Below is a table with the results of a blood typing test. Identify the blood types based on the reaction with the antisera.

Sample / Result with anti-A / Result with anti-B / Result with anti-Rh / Blood Type
1 / agglutination / no reaction / no reaction
2 / no reaction / no reaction / agglutination
3 / no reaction / agglutination / no reaction
4 / agglutination / agglutination / agglutination