miniPCR bio™ Electrophoresis Forensics Lab. Wrongfully Convicted? Instructor's and Student's Guide
Version: 1.1 - Release February 2022 - © 2022 by miniPCR bio™
Student's Guide
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Today's lab
Only recently has DNA analysis become standard in criminal investigations. For cases that predate
the use of DNA analysis, sometimes DNA can still be collected from physical evidence stored for
an extended period. In many real-world law enforcement investigations, new DNA analysis of old
evidence has cracked cold cases that were previously unsolvable. In other cases, new DNA analysis
from closed cases has cleared wrongly convicted individuals. Today you will use gel electrophoresis
to determine if DNA from an incarcerated individual matches newly extracted DNA from old crime
scene evidence.
The case
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In 1999, a young man was brutally attacked and strangled in an alley. The victim was found
unconscious and severely injured, but he survived. The victim told the police that while the
perpetrator had been wearing a ski mask, he was very tall and had a chipped front tooth. A ski mask
found in a dumpster in the alley was collected as evidence.
Later that week, an officer spotted an individual, J.M., walking down the street near the crime scene.
J.M. resembled the description of the perpetrator, and he was brought in for questioning. Although
the victim had never seen the perpetrator's face because of the mask, he identified J.M. in a live
lineup and testified in court that he was certain that J.M. was the attacker because of his distinctive
chipped front tooth. In addition, several hairs were retrieved from the ski mask found in the alley.
Microscopic analysis of the hair from the ski mask was said to match a hair sample collected from
J.M. Based on this evidence, the jury found J.M. guilty.
J.M. was convicted of attempted homicide and is currently serving a life sentence. J.M. has always
maintained his innocence, and after years of appeals, the court has approved his request for DNA
analysis of the evidence from his case. You have been sent DNA from four samples: a cheek swab
from J.M., a cheek swab from the victim, and DNA from two hairs collected from the ski mask. The
DNA you will test today represents the result of PCR amplification at a single STR location in the
genome.
It's your job to ensure that the criminal justice system did not fail in this case. Can you prove J.M. to
be innocent? Or will the evidence only implicate him further?
