Prev Next

Notes for the Instructor

A toxicologist is a scientist who studies the effects of chemicals in living things. Toxicologists will be called into an investigation if a victim is found injured or dead and alcohol, drugs or poisons are suspected. Toxicologists will also assist during investigations where unknown substances are found at the crime scene – for example, in medicine bottles or any loose powders at the scene. Toxicologists must identify the substances found, determine how much of the substance is present, and explain what effect(s) the substances may have on a person or its relationship, if any, to the crime.

When someone is suspected of being poisoned with an unknown substance, the toxicologist will begin by recording physical symptoms of the person. Are they conscious? Groggy? Extremely agitated? These symptoms are clues that will help identify the substance.

Next, toxicologists can test the person’s body to learn more about the unknown substances. Alcohol, drugs and poisons can be detected in the blood or urine of a person. Urine samples are preferred because drugs show up at higher levels and last longer in urine than they do in blood. Additionally, hair can tell the story of drugs or poisons. Chemicals in the bloodstream can be transferred to growing hair.

Toxicologists can look for substances in living or dead people. However, samples taken from a living person are more difficult to interpret than samples taken from a deceased individual. This is because a living person’s drug levels drop rapidly as the drug or poison is processed in their body and eliminated. In contrast, drug and poison levels do not change much after death since the body systems are no longer working.

In this activity, students will analyze the chemical characteristics of four unknown white powders. Although all of these substances are non-toxic, household items, this is a great time to teach your students lab safety.

  1. Never eat anything you are using in a science lab.
  2. Follow procedures exactly to ensure results.
  3. Properly dispose of all materials at the end of the lab.

Students will be analyzing the unknown white substance found at the cookie jar crime scene. They will also analyze four samples connected to the suspects. Through observation, comparing and contrasting, students will attempt to match one of these substances found at the crime scene to a suspect.

Again, this is an example of class evidence, or evidence that can help narrow down the field of suspects, but cannot pinpoint a specific individual. The white powder is also what is known as trace evidence. Trace evidence is any small amount of hair, skin, fabric or other material that may link a suspect to a crime scene.

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.