Forensics

Experiment Title: 

What Happened?

Objective:

Learn what forensic science truly is and how it can be applied to many situations

Background:

Forensic Science is the application of many scientific disciplines to look at physical and digital (evidence) to determine what happened during a particular event. Imagine for a minute that a team of four people are baking a tray of cookies. The tray gets dropped and the cookies fall on the ground. What would specific parts of the cookie patterns and composition tell us? We might be interested in some of the following types of questions:

1. Did the cookie tray fall on the ground or was it thrown?
2. Were the cookies raw or were they cooked?
3. How long ago did the tray drop occur?
4. If there is more than one type of cookie or more than one tray, can we determine where each type/tray came from?
5. Why did the cookie drop occur?

These questions and others help to answer the question of what happened, but in order to answer them we have to carefully preserve the scene of the accident and collect relevant evidence to each question. The significance of why a particular event happened may be important too.

Let’s consider for a moment each question, and the types of physical evidence that we might collect and what it might tell us.

• Did the cookie tray fall on the ground or was it thrown?

Two pieces of physical evidence are the tray(s) and the cookie(s). We might not be able to say precisely what happened, but evidence might influence us in one direction or another. If the cookie tray landed right side up and many of the cookies remained on or near the tray this might suggest that the tray was simply dropped. An upside down tray with cookies in a relatively small area (potentially with a significant number under the tray) might tell us that someone attempted to catch the tray as it fell, but perhaps tipped it mid-air.

A wide dispersion of cookies might tell us that the tray flew with significant force, possibly due to someone tripping and flinging the tray.  We might expect to see cookies spread in a single direction or radially from a single point. If we found a wide dispersion of cookies uniformly around a central point, we would have to consider possible reasons that occurred. Whether the cookies appear to be mostly whole, mostly broken, or some other combination is relevant as well. These measurements would be highly dependent on the type of cookie, whether the dough was cooked, and whether the pan was greased or significant fat content was present in the cookie to prevent it from sticking to the pan. This brings us to a second question:

• Were the cookies raw or were they cooked?

Raw cookie dough tends to be soft and easily deformable. Many cookies are crunchy when cooked, or at least can’t be readily molded into different shapes. Cookie dough is, on average, stickier than cooked cookies. Cookie dough also has a higher water content and density than a cooked cookie. Clues such as weight, hardness/deformability, and possibly temperature can tell us important details about the state of the cookies at the time of the accident and these details can also have important implications for other areas of the investigation (such as whether the tray was dropped or thrown). Let’s consider a couple of important time-dependent elements for the third question:

• How long ago did the tray drop occur?

In determining when the tray drop occurred, we might want to know more about whether the cookies were cooked or raw. If we identify that the cookies were cooked, we might look at aspects such as temperature (a higher temperature than the surrounding environment might suggest that they were recently cooked) or moisture content (a uniform temperature with the surrounding environment and a higher water content may suggest the cookies had been cooked for some time). For raw cookie dough, if notable signs of spoilage have occurred (ex. Molds/fungus, rotten smell, infestation/consumption by bugs and rodents), this might suggest a longer time has passed. Spoilage is dependent both on the ingredients of the cookies and the environment. Is trace evidence, such as fibers and hair, present? Is any sediment, including soil, dust, or sawdust present? Chemical traces from the cookies can help identify what was in them to help inform the answers to our other questions.

• If there is more than one type of cookie or more than one tray, can we determine where each type/tray came from?

Different types of cookies have different signatures. Chocolate chip cookies are notably different from oatmeal, which are also notably different from plain sugar cookies or snickerdoodles. Characteristics such as color, texture, chemical composition, temperature, moisture content, etc can be used to help identify whether there are multiple types of cookies (or even two batches of the same type of cookie) involved in the accident. If multiple types of cookies are found, potentially too many for a single bake, and a single tray is found, we might wonder if a second tray was removed from the area.

Very rarely can a specific investigative question be answered in isolation. It’s important as investigators to examine all of the physical, digital, and human evidence to determine what happened. Collecting and analyzing evidence before making a conclusion is important to ensure that we provide a fair and unbiased assessment of what happened (Making a conclusion before evaluating all of the evidence may influence how we collect future evidence and prevent us from considering evidence that does not support our conclusion).

• Why did the cookie drop occur?

This question may or may not be possible to answer from the physical and digital evidence that we have collected and analyzed before. We may have to combine physical evidence with information provided by people involved in the situation to develop why the cookie tray drop occurred. Was it an accident or was it intentional? Was one person involved or more than one person? Were other elements of the environment (slippery floors, animals, work surfaces) involved? Identifying why an event occurred may help us address the event and possibly prevent it from happening again in the future.

Forensic thought processes are important for troubleshooting experiments and explaining unusual results. Reconstruction of a timeline of events and all of the physical, digital, and human evidence collected can be highly informative for answering the basic what, when, where, how, and why of a specific situation. 

Materials

For the first exercise you will need the following items:

• Plastic cup
• Plastic beads (10 - 15)

Experimental Procedure

In this experiment you will be asked to evaluate several pieces of physical evidence and provided material to experimentally recreate aspects of the evidence to help explain it. The following four bead patterns were observed: 

For each of the bead patterns, use the cup and beads to work to recreate the pattern (note that a similar pattern is sufficient and will be very difficult to reproduce it exactly). Your goal is to develop answers to the following questions:

1. Describe (or draw) what happened and how it likely happened
1. Example: The cup was tipped lightly, but not with excessive force and this caused the beads to… and the cup to…).
2. Describe (or draw) when parts of the bead pattern likely occurred
1. Example: The beads closest to the cup stopped first while the beads furthest stopped last. The cup stopped while the beads were still moving…
3. Describe (or draw) where parts of the bead pattern occurred
1. Example: Most beads were clustered between 2 and 4 cup widths away from the cup. A couple of beads were closer than 2 cup widths and a couple were further than 4 cup widths.
4. Describe (or draw) why the bead pattern occurred the way that it did
1. Ex. Most of the beads started with a similar speed and since they mostly moved in similar ways they ended up in almost the same area.

Most people would assume that the cup and beads were set into motion near the same time. How would your answers to the above questions change if:

1. It is known that the cup contained all of the beads at the beginning
2. It is known that the cup was set first, and then the beads
3. It is known that the beads were set first, and then the cup
4. It is known that some of the beads are set in their final positions, then the cup is set, then the remainder of the beads are placed.

Conclusions 

Forensic Science can be used to help a student, parent or teacher to calmly and rationally assess what has happened in an instance without questioning the who of a situation. When forensic science is applied one can learn a lot about a situation and create reasonable hypotheses for what circumstances created the final outcome. Today the students used beads to pretend to spill a tray of cookies and to see how different drops or throws can create different bead patterns.

Extension Activities

Move on from the beads and try a larger scenario and see how it works out. In this you could use play dough to act as raw cookie dough, or use model magic to act as freshly baked cookies that have cooled but are still somewhat elastic. Try the same experiment using these different mediums and see how the cookie dispersal might change with the different cookie states.

Make it your own

Now go home and create your own forensic scene (with your parents permission, this might be best done outside) and see if your parents or friends can help unravel the scene that you have created. Remember that forensic science itself is not about who did it and why they did it, but is focused on what happened (when, how, etc...).