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Notes for the Instructor

You have now arrived at the moment to assemble all of the evidence in The Cookie Jar Mystery in order to determine the guilty party. Who broke the cookie jar? We’ve amassed, over the course of 11 lessons, an astonishing array of evidence. Not only are there fingerprints, hair samples, and blood types, there is pollen, DNA, ink pens, fibers, and even handwriting! Rarely, of course, will so much evidence be available at any single crime scene.

But, is all evidence created equal? During this lesson students will determine the value of each piece of evidence. They will realize that some evidence is purely circumstantial—it suggests only the presence of a suspect at the crime scene, not his or her inevitable guilt. They will also be asked to remember the distinction between class evidence – evidence that points to a group of people – and unique evidence – evidence that points to one specific person.

Here are some key points to guide students as they weigh the evidence. Use these as discussion prompts if students get stalled:

• Check the location of all the suspects during the time the cookie jar was broken. Who had easy access to Mrs. Randall’s room? Did any suspects have a clear line of sight to the room? (Suspect 4 was in a position to see who entered and left Mrs. Randall’s room. She would recognize her sister, suspect #3, who had an easy, direct route from the playground to Mrs. Randall’s room.)

• Look back on the suspects’ statements. Did anyone’s statement seem like they were lying or hiding something? (Suspect #3 was defensive and evasive in her statement, “I didn’t go back into school after that, why would I? Went home and got something to eat. That was about it.” She also left out the pronoun “I”, verbally separating herself from the crime. She had a means to commit the crime by sneaking in the playground door. Hunger was her motive. She had an opportunity because only her sister was around – someone that she could trust not to tell on her.)

• How strong is the evidence for the remaining suspects?

  • Suspect #1 __________________is not a very likely suspect. Although pollen evidence and fibers from his clothes were found, they don’t indicate his presence during the breaking of the cookie jar.
  • Suspect #2 ___________________admitted that she often carried the cookie jar. Her fingerprints, and even hair and fibers from her clothing, might be on the jar. This does not provide enough evidence to link her to the cookie jar at the time it was broken.
  • Suspect #3, _________________on the other hand, left her blood and DNA on the cookie jar. This happened when the jar was breaking. These pieces of evidence are unique.
  • Suspect #4, __________________suspect 3’s sister, admits writing the note, and so the chromatography test should be positive for her pen. She also admits trying a bite of a cookie. It is possible that she knows who broke the cookie jar but will not tell. Notice the pronoun changed to “we” in the suspect statement.

As your students begin to work through the crime, encourage them to talk it through with their partner. When two students disagree on a point, encourage them to find evidence that supports their claim.

The activities in this lesson address Next Generation Science Standards practices of Planning and Carrying Out Investigations and Analyzing and Interpreting Data. In addition, they address Common Core Learning Standards. See the appendix on page 105 for more details.