©OPCME Allison Domzalski 2011. (DNA); Shutterstock.com (All Other Images)

I Solve Crimes With Science

Craig O'Connor uncovers clues that help close a case

By Alex Lim-Chua Wee

From the February 2025 Issue

Learning Objective: Students will summarize how and why a forensic scientist uses DNA evidence to solve crimes.

Lexile: 730L; 520L

Key Focus Area: Traits,

Other Focus Areas: Geometry

As you read, think about how forensic scientists analyze clues as part of their job.

ocme.nyc.gov

Craig O’Connor

A half-eaten pizza crust. An empty soda can. A plate of chicken bones. To you, they’re just someone’s leftovers. But to Craig O’Connor, they could hold the secrets to solving a crime.

O’Connor is a forensic scientist. He works at one of the nation’s largest crime labs in New York City. The lab studies evidence from crime scenes. Its findings support the work of the city’s police department and other law enforcement agencies.

O’Connor works on a team with 200 other forensic scientists and investigators. Each year, they receive nearly 10,000 cases! Once they get evidence collected by the police, their goal is to study the evidence, learn important information from it, and help solve the crime. He recently spoke with Scholastic about his work.

A half-eaten pizza crust. An empty soda can. A plate of chicken bones. They might seem like just someone’s leftovers. But not to Craig O’Connor. They could hold secrets to solving a crime.

O’Connor is a forensic scientist. He works at a crime lab. It’s one of the nation’s largest. It’s in New York City. The lab studies evidence from crime scenes. These clues help the police.

O’Connor works on a team. It’s made up of 200 other scientists. They get nearly 10,000 cases a year! Police gather evidence. They send it to the lab. The lab studies the clues. They share what they learn. This can help solve a crime. O’Connor recently spoke with Scholastic about his work.

What led you to become a forensic scientist?

As a kid growing up in Connecticut, I always liked science and solving puzzles. With puzzles, you have all the pieces. The challenge is figuring out how they fit together. This feels a bit like how science works. You start with a question, and you need to find the best way to get an answer. What materials do you need? What experiments should you do? I always liked using my brain that way.

Watching crime shows on TV is what got me interested in forensic science. I wanted to learn more about using science to help victims of crimes.

I spent years studying genetics in school. That’s the study of how traits are passed down through families. Then I moved to New York City to work in a crime lab.

I grew up in Connecticut. I always liked science as a kid. And I like solving puzzles. You have all the pieces with puzzles. But you have to figure out how they fit together. This feels a bit like how science works. You start with a question. And you need to find the best way to answer it. What materials do you need? What experiments should you do? I always liked using my brain that way.

I watched crime shows on TV. That got me interested in forensic science. I wanted to learn more about using science to help victims of crimes.

I spent years studying genetics in school. That’s the study of traits. They are passed down through families. Then I moved to New York City to work in a crime lab.

What do you look for when examining evidence?

Our lab focuses on finding DNA. This substance is found in every cell in your body. It’s in skin, hair, and saliva. Everyone’s DNA is unique to them.

Forensic scientists have a saying: “Every contact leaves a trace.” Did you know you shed hundreds of thousands of skin cells every day? Everything you touch has a bit of you left behind. When we find that DNA, it can help tell us who an item belonged to and who else touched it.

Our lab focuses on collecting DNA. It is found in every cell in your body. It’s in skin, hair, and spit. Everyone’s DNA is special to them.

Forensic scientists have a saying. It’s that “every contact leaves a trace.” You shed hundreds of thousands of skin cells every day. Everything you touch has a bit of you left behind. We find that DNA. It can help tell us who an item belonged to. And it can tell us who else touched it.

Zoom In on DNA!

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Every cell in your body contains material called DNA. It’s passed down from your parents. DNA contains shorter sections called genes. Each gene is like a sentence in your body’s instruction manual. Your genes determine traits like your eye and hair color.

Zoom In on DNA!

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How do you find DNA?

Let’s say we’re studying a pizza crust. We look at the bite marks first. Then we use a cotton swab to collect a saliva sample. We put the sample in a test tube, then add in a mix of chemicals. These chemicals help break down the protective layer in the cells. Once this layer has broken down and dissolved, we can take out the cell’s DNA.

Next, we need more copies of the DNA to analyze it. We add more chemicals to make copies.

Finally, we use a tool called a genetic analyzer. This translates the DNA into a special kind of graph that lets us compare DNA from different people. This tells us who was likely at a place—and who might have committed the crime. Detectives combine this information with other evidence, like fingerprints and footprints, to learn how a crime might have happened.

Let’s say we’re studying a pizza crust. We look at the bite marks first. Then we use a cotton swab to collect a sample of spit. We put the sample in a test tube. Then we add in a mix of chemicals. They help break down the cells’ layers. Then we can take out the cell’s DNA.

Next, we need more of the DNA to study. We add more chemicals to make copies. Finally, we use a tool that reads the DNA. It creates a special kind of graph. We use it to compare DNA from different people. This tells us who was likely at a place. And it may tell us who might have carried out the crime. Detectives use this information. They also use other evidence. This includes fingerprints and footprints. They try to learn how a crime might have happened.

What’s the most challenging part of your job?

Many cases can be upsetting. It’s natural to feel sad or angry that these crimes happened. It’s important that we, as scientists, stay focused. Our job is to help find answers and bring justice to people who have been hurt.

Many cases can be upsetting. It’s natural to feel sad or angry that these crimes happened. But we try to stay focused. Our job is to help find answers. Then we can bring justice to people who have been hurt.

How realistic are most of the TV shows with forensic scientists solving crimes?

Characters on crime science shows usually work on one case at a time. We often work on thousands in real life. It can also take us 30 to 60 days to get testing results. You often see it all get solved the next day on TV shows. I wish it were that fast and easy.

Math on the Job

Investigators sometimes make a grid of a crime scene, like the one above, to make sure no clues get overlooked. Imagine a suspect left evidence at this scene. Each item has DNA from the suspect on it.

Use the coordinate plane and crime scene to answer the questions below.

The door is near the coordinates (0,0). Plot and label this point D.

Write an ordered pair for the coordinates of the pizza crust.

A hat is at (4,3). Plot the point and label it with an H.

A cell phone is at (7,8). Plot the point and label it with a C.

Draw a line connecting each point in a path from the door to the trophies. What do you think the suspect did?

Math on the Job

Use the coordinate plane and crime scene to answer the questions below.

The door is near the coordinates (0,0). Plot and label this point D.

Write an ordered pair for the coordinates of the pizza crust.

A hat is at (4,3). Plot the point and label it with an H.

A cell phone is at (7,8). Plot the point and label it with a C.

Draw a line connecting each point in a path from the door to the trophies. What do you think the suspect did?

video (1)

Slideshows (1)

Activities (4)

Answer Key (1)

1. PREPARE TO READ (5 minutes)
Discuss jobs and skills involved in solving crimes.

Ask: What jobs deal with solving crimes? (e.g., police officer or detective) Explain that after evidence is gathered by law enforcement, it may be sent to a lab. Then an expert called a forensic scientist can study it for clues. Ask: What skills might be important for examining evidence? (e.g., observing closely; recording important details; measuring accurately)

2. READ AND SUMMARIZE (25 minutes)
Read the article and synthesize information about working as a forensic scientist.

Tell students they’re going to read about someone who solves crimes with science. Preview vocabulary with the Vocabulary Slideshow. Project the article and read it aloud while students follow along in their magazines.

After Craig O’Connor’s response to each question, pause to note important points. Discuss what students notice and think about the visuals. When discussing “Types of Evidence Collected,” ask students to guess the purpose of the tool being used on the shoe and explain their thinking to a partner. Tell them it’s a digital caliper used to take measurements—in this case it’s measuring part of the boot’s tread (the pattern on the bottom of a shoe).

Tell students that detectives must keep track of where evidence is collected to help forensic scientists do their jobs. Preview the article’s “Math on the Job” sidebar, reading the introduction and reviewing coordinate grid math if needed. Have student pairs complete the activity. Then reconvene to discuss question 5.

3. RESPOND TO READING (45 minutes)
Collect and analyze evidence to figure out what happened in a mysterious scene.

The activity Collect and Analyze Evidence requires advance preparation to stage the scene. See page 1 for directions to set up your stolen snack and the clues. As students investigate, encourage them to observe evidence first, then draw conclusions after examining all the evidence. Discuss what they think happened and why.

Tell students that they’ve now practiced both math and science skills related to the job of a forensic scientist, and they’re going to use those experiences to evaluate this career. Preview the Cool STEM Jobs Spotlight activity. Have students complete the activity independently.

STEM INTEGRATION

MATH: Use coordinates to evaluate evidence (CCSS Math: 5.G.A.1, 5.G.A.2)

Share the More Math on the Job activity. If needed, guide students through the “Need a Hand?” box (page 3). Then have students work independently or with a partner to complete the questions. Reconvene to discuss their answers.

HANDS-ON: Observe patterns in fingerprints and lift them (NGSS: LS4.B, ETS2.B)

Prepare in advance for the activities here: https://www.scholastic.com/parents/school-success/learning-toolkit-blog/be-fingerprint-detective.html. Distribute magnifying glasses. Have students look for the ridges on their fingers—their fingerprints. Explain that in addition to DNA, fingerprints can be valuable evidence for forensic scientists. Distribute paper, pencil, and tape and show students how to do the first activity, “How to Study Fingerprints.” Then share examples of the three main patterns: loop, whorl, and arch. Have students examine their prints with the magnifier to see if they can identify any of these patterns. To take it further, try the second activity, “To Lift Prints.”