In 1993, in a murder trial in Arizona, a lawyer had an interesting remark- he said that he is probably the only lawyer to have lost the case to a tree!
Let us hear that story…
In 1992, on the outskirts of Phoenix, Arizona, a woman was found murdered. There was hardly any evidence left by the murderer. However, there is no such thing as a perfect crime. Read on to find out how forensic analysis led to justice.
At the crime scene, forensic investigators found a syringe, some pieces of clothing and a pager that did not belong to the victim (It’s an old case. Pagers were a thing back then, fellow millennials). Homicide detective Charlie Norton noticed fresh abrasion on a Palo verde tree at the crime spot, and took some bean pods off that particular tree.
A fingerprint search helped identify the victim as Denise Johnson. Denise was a single mother of two and lived in ‘the projects’.
The pager was traced to a truck driver Mark Bogan. When confronted, Bogan said that Denise had requested him for a ride and then tried to steal some things from him when he dropped her. He said that he took his wallet back from her but later noticed that his pager was missing.
Scratches on Bogan’s face did not escape the investigator’s eyes while they were interrogating him. However, no traces of blood or skin cells were found under Denise’s nails. Her autopsy revealed that she had died from ‘asphyxiation due to strangulation’.
When the investigator’s visited Bogan’s truck, there was no evidence to suggest that he was involved in the crime- no fingerprints, blood, or hair. However, in the back of the truck they found two bean pods from a Palo verde tree.
The only way to prove that Bogan was at the crime scene, was to prove that the pods in his truck came from that same tree. And that was tough, because obviously, there is not just one such tree there! Arizona has thousands of Palo verde trees.
Now, DNA forensics involving animals and humans is common place. But plants? Not at all. In 1980, Dr Alec Jeffreys developed the technique called genetic fingerprinting that was used as evidence to solve cases, but plant DNA analysis had never been admitted as evidence before.
This is where Dr Timothy Helentjaris came into the picture. A professor at the University of Arizona, Dr Timothy specialized in plant genetics. Since no one had extensively studied Palo verde trees before, Restriction Fragment Length Polymorphism (RFLP)- a DNA analysis technique used frequently for human DNA, could not be performed. Moreover, not enough DNA could be extracted. Hence Dr Helentjaris used the Randomly Amplified Polymorphic DNA (RAPD) technique which works despite low DNA concentration, on any biological sample.
In RAPD, the seeds are removed from the pods and ground to a fine powder. The DNA sample being too low to be analysed needs to be amplified by Polymerase Chain Reaction (PCR) which multiplies the DNA millions of times within a few hours. That sample is then run on an agarose electrophoresis gel and the gel is exposed to UV light to enable visualisation of DNA as short, horizontal bands. The band pattern for every individual is unique. This is the equivalent of a QR code, called a genetic fingerprint.
Dr Helentjaris found that the DNA band pattern of seeds from both pods in the truck, matched each other. Furthermore, they also matched the DNA band pattern of the seeds from the pods that detective Norton had taken from the tree at the crime scene! When a similar analysis was carried out with DNA from other seed pods in the neighbourhood, there was no perfect match, proving their hunch right- about the pods in Bogan’s truck belonging to the tree at the crime scene.
The judge permitted the results of this DNA analysis to be submitted as evidence. Something that was unprecedented. The jury agreed that this piece of evidence wasn’t circumstantial and found Mark Bogan guilty of first degree murder, sentencing him to 25 year imprisonment.
And thus, despite having no obvious evidence of the victim, Bogan’s lawyer lost his case to the unique seed pods of the Palo verde tree!
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