Miss Day 1? Check it out here
Since Monday, our student detectives have collected blood, DNA, handwriting, and ink samples from all of our suspects.
They all look so innocent!
Wednesday in class they analyzed their crime scene and suspect evidence to see if they would determine the culprit!
Blood typing was done to determine if all of the blood at the crime scene (two locations) was from the victim or if someone else’s blood was present. In this method, the blood samples are mixed with antibodies that bind to chemical signals on our red blood cells that determine our blood type (A, B, O, AB; Rh negative or positive). Changes in the color and clotting indicate the blood type.
Raquel loading the agarose gel
The same group also used a method called Restriction Fragment Length Polymorphism (RFLP) to individualize the DNA left at the crime scene on the pop can. Each human shares about 99.9% of their DNA with other humans – this is the DNA that’s used to make proteins that we all have. But 0.1% of our DNA is unique. While this may
Loaded and ready to run!
seem like a tiny difference, it comes out to about 3 million(!!) different bases – the building blocks of DNA. RFLP exploits these differences by using enzymes (restriction enzymes) that cut up DNA into smaller pieces. Everyone’s DNA will produce fragments of different lengths, which can be visualized on an agarose gel and compared to the evidence (polymorphism just means different forms – which these fragments are among a group of people). Tune in next Wednesday to see what the gel looked like when it was finished!
One group of detectives got a lesson in how weird it is to take someone’s fingerprints! And how hard it is to compare suspect fingerprints to partial prints found at a crime scene. They were diligent and are close to catching the perpetrator!
The document analysis group set out first to compare handwriting samples to the note they found at the crime scene. Distinctive handwriting can be a dead giveaway in some cases – what about in this case?
TLC of ink samples
They also compared ink from the note to the pen samples they collected from suspects using a method called thin-layer chromatography (TLC). This method uses solvents like methanol (mixed here 2:1 with water) to separate components of a substance like ink which is composed of dyes or pigments. Even pens that all use black ink can look different when separated by TLC due to different formulations used by manufacturers.
Sally applying the powder to the chemical-loaded PADs
Our last group was trying to figure out the identity of the white powder left at the scene. To do this, they use a combination of solution tests and chemical tests utilizing paper analytical devices (PADs), which is research that Dr. Barstis does in collaboration with the University of Notre Dame (PADs project). After putting drops of chemicals on the PADs in the white lanes, they scrape the powder across the whole PAD and then stand the PAD in a little bit of water.
The paper wicks up the water, which carries the powder to the chemical and the reaction and possible color change takes place. Color changes can indicate the makeup of the powder – for example, the dark purple spot in the middle lane of the PAD on the right tells the group one major component of the white powder.
So what were the results of all of these analyses? Tune in next Wednesday to see if we have identified a single perpetrator from our evidence. During class on Wednesday, each group will present their findings to a jury of the possible suspect’s peers (a team of science and humanities profs) who will vote on whether they can convict based on the evidence.
Authorized Personnel Only!
Today, on her way back from teaching class in Spes Unica, Dr. Haas took a shortcut through SC 113 (Biochemistry lab) in the dark and ran into an unknown assailant who knocked her down and rushed out of the room. She suffered from a bleeding head wound* and could not identify the assailant. The task of the students of CHEM 424 (Advanced Biochemistry) this week and next is to identify this unknown perpetrator and bring him or her to justice using the evidence left at the crime scene.
The crime scene from different angles
Dr. Fishovitz was the first officer to arrive and secured the scene and established a perimeter before the other detectives arrived. Before entering the room, everyone had be logged in and photographs of the soles of their shoes were taken (to rule out any shoeprints they might leave on the dusty floor, thanks renovations!).
The detectives first took a survey of the crime scene and pointed out any obvious evidence they could find:
1. A white salt-like powder on the bench-top and an open glass vial with a plastic lid
2. A knocked-over garbage can with torn paper spilling out
3. A torn piece of white paper with something written in black ink on it “like a”
4. An empty Pepsi can on its side
5. Blood drops (4)
6. Blood drop on a drawer handle
The next thing we did was brainstorm about some trace evidence that may be around that we couldn’t see – like DNA, fingerprints, hairs or fibers. It was decided that the Pepsi can could have fingerprints on it and DNA from saliva around the opening. It would be tested for both later. Other possible sources of fingerprints included the benchtop, the glass vial, the paper from the garbage can, and the exit door.
The class split itself up into groups of 4. Each group would collect and analyze specific evidence. Group 1 (Sally, Natalie, Katy G, and Adrienne) would be working on the unknown white powder.
Natalie and Sally collecting the white powder. After transferring it to a glass vial, they put the vial into a zip-top bag and filled out the evidence tag.
Detectives bagged and tagged the evidence they collected and filled out the chain of custody each time the evidence changed hands
Group 2 (Jenna D, Katy H, Cara, and Raquel) are analyzing the DNA and blood samples.
Katy very carefully resuspending dried DNA from the mouth of the pop can. After collecting the liquid, she transferred it to a microcentrifuge tube and bagged and tagged it
Annie collecting the dried blood with a swab. She would later pass this evidence off to Cara, Katy, Jenna, and Raquel for analysis
Group 3 (Annie, Marie, Cinthya, Carrie) are in charge of document analysis, including analyzing the handwriting and ink makeup.
Annie collecting the torn paper from the garbage can. Her group would keep and analyze the piece with writing on it, but pass off the blank pieces to the fingerprint group to check for latent prints
Group 4 (Liz, Claire, Emma, Jenna B) are the fingerprinting gurus! They had the hardest job by far when it came to collecting evidence from the crime scene. If fingerprints are left by transferring things like paint or blood, or if they’re left by impressions in dust or soft substances like putty or gum, they’re pretty easy to spot, but most fingerprints are latent (invisible) prints. This means they are not easily visible to the naked eye and take some work to find! This group used fingerprint powder to dust for prints on the glass vial, the pop can, the bench-top, and the glass window in the door. After a lot of dusting – they were successful! They also used a chemical test – the ninhydrin test. This is a chemical spray that will adhere to fingerprints on porous surfaces such as paper and leave and purple or brown print. They tested the torn paper using this method but no prints were found on the paper.
Liz dusting for prints on the pop can. A couple showed up but they were hard to transfer!
Jenna dusting the bench-top for prints – again, a couple of prints showed up but were very hard to transfer cleanly!
They got a few good prints from the crime scene!
After collecting all of the evidence from the crime scene, the detectives set out to collect samples from the suspects (the faculty and staff of the Chemistry/Physics department). They would collect blood samples, DNA samples, handwriting samples, pens, and fingerprints from each suspect. If they were lucky, the suspect didn’t refuse to submit DNA or a pen!
On Wednesday, they’ll work on comparing the crime scene evidence to samples from suspects and narrow down the list of possible perpetrators so that next week they can present one possibility to the class and jury.
*Disclaimer: No faculty, staff, or students were hurt in the staging of this crime scene. All blood and DNA samples are simulated.
To be continued on Wednesday… (Day 2 up now!)