Crime File

THE DENISE JOHNSON CAE The Seed Pods Convinction

It was the first case in the world in which plant DNA was admitted in evidence to buttress circumstantial evidence to secure a conviction. HEMRAJ SINGH tells the story of an unusual investigation.


On May 3, 1992, a motorcyclist came across the dead body of a woman in a deserted area on the outskirts of Phoenix in Maricopa County, Arizona. He reported the gruesome find to the police forthwith. The woman had been beaten up, bound and strangled to death quite apparently. There were no clothes on the body of the victim except a tank top that had been pulled up to her neck, and wrapped around her neck was a t-shirt that almost certainly belonged to the victim and had probably been used to strangle her.

The condition of the body raised a strong suspicion of rape. Her ankles had shoe laces and a string with which they seemed to have been loosely tied. The investigators also found a syringe and several pieces of clothing lying around the body. While the investigators were still working on the crime scene, they heard an electronic device beep repeatedly. They looked around and found a pager lying nearby, which became their first workable piece of evidence. After the evidence was collected from the scene, the body was sent to the medical examiner for autopsy and identification of the victim. A fingerprint search found a match. The victim was a 30-year-old Denise Johnson, a single mother of two kids.

Denise was born and raised in Phoenix. But as she grew up she was drawn to the wrong kind of people – the kind that are almost never good news. Drugs, alcohol and partying was a way of life with Denise, who earned her living on the street mostly by selling drugs and shortchanging truck drivers on it. Given the life Denise lived, there were a wide range of scenarios that could land her where she was found. So, looking into her life did not readily lead the investigators to a prime suspect. They looked into the pager and found that it belonged to one Mark Bogan, a local truck driver. He was called in for questioning.

Bogan told the investigators that on May 2, 1992, on his way back home from work, he stopped to make a phone call, which was when Denise approached him and requested a ride to the interstate. Bogan obliged. While they were driving, Denise made some sexual overtures, which led to Bogan’s stopping the vehicle at a deserted spot and their having consensual sex in the cabin of the truck. However, that was not the end of it. Bogan claimed that while he was dropping her off, she made a move to steal his things from the dashboard but was caught in the act. Bogan wrenched his wallet back after a minor fight. She stepped out of the vehicle and walked away on foot. That was the last time Bogan said he saw her. As for the pager, Bogan told the investigators that he realized that the device was missing only in the morning. He thought he had dropped it somewhere and called the pager company to report it lost.

However, during the questioning the investigators couldn’t help notice scratch marks on the side of Bogan’s face suggesting a physical fight, and such scratches could leave blood or skin under Denise’s nails, if the injury was caused during the scuffle between the two of them. But the autopsy did not find any skin or blood under Denise’s fingernails. Autopsy confirmed that Denise had been strangled to death and that she was high on cocaine at the time of her death, but there were no signs of any sexual activity. There was no semen, no foreign hair or saliva anywhere on her body. She had not been raped as the state of the body had suggested. There was nothing to connect Bogan with the crime either. At this point there was nothing left for the investigators to pursue – no leads and no suspects.

A day after Denise’s body had been found, Homicide Detective Charles Norton, to whom the case had been assigned, visited the crime scene to familiarize himself with the area where the body had been found and to look for evidence and clues that the first responders or the crime scene investigators might have missed. Detective Norton came across a fresh abrasion on one of the low branches of a Palo Verde tree. It was quite possible that the abrasion on the tree had something to do with the crime because the area was otherwise deserted and the likelihood of human activity was very slim. It could only be a major coincidence by which the fresh abrasion was caused by some happenstance separate and unconnected with Denise’s murder around the same time as the murder. So, the likelihood of the two things being connected was fairly high. Detective Norton clicked a picture of the abrasion and plucked a few beans off the tree for further investigation.

Mark Bogan’s truck had been thoroughly checked for relevant evidence. No blood, no semen, no saliva, no fingerprints or anything else connecting Bogan or the truck to the crime was found. There was no physical evidence to even suggest that Denise Johnson had hitched a ride on the truck. However, the investigators did find two bean pods from a Palo Verde tree in the back of the truck. The pods were photographed and stored as evidence.

The discovery of bean pods gave rise to the theory that Bogan’s truck scraped against the Palo Verde tree leaving an abrasion on the tree and making the bean pods drop into the truck as he drove away from the crime scene. Bogan had claimed that he had dropped Denise on the road and had driven away whereas the body had been found far off the road and Bogan could have had no conceivable reason to be at the crime scene if he had nothing to do with Denise’s murder. However, the theory could hold only and only if it could be established that the bean pods found in Bogan’s truck were from the Palo Verde tree at the crime scene. It was not an easy task because there are a large number of Palo Verde trees in the State of Arizona. After all, it is not for no reason that Palo Verde tree was designated the official state tree of Arizona on April 9, 1954 by a state legislation to that effect. So, the only way was to try matching plant DNA, if that was possible at all.

The next challenge was to find someone who could actually do it for them. So, the detective started calling every such person who he thought could help him with it. Nobody had done it before for sure and there were many who thought it was not even possible. Then there were some who thought it could be done but the expenses involved would be astronomical. Finally, after having called the scientists across the United States, the detective found help at the University of Arizona itself. A plant geneticist agreed to lend a helping hand. He used a technique called Randomly Amplified Polymorphic DNA (RAPD) technique to match the two sets of plant DNAs – one from the pods found in Bogan’s truck and the other from the pods taken as sample by the detective. The RAPD test is different from the Restriction Fragment Length Polymorphism (RFLP), which is used to analyze and match the human DNA.

The DNA analysis proved that the pods found in the pickup truck owned by Mark Bogan came from the tree at the crime scene. However, since plant DNA had never been used as evidence in a court of law, the prosecution needed to show that all Palo Verde tree had distinct DNA profile and the pods in Bogan’s truck could not be there by a rare coincidence. So, samples from some one hundred Palo Verde trees in Arizona were collected and given to the same plant geneticist. In order to make the test harder and confusing, the investigators also got the samples from the Palo Verde tree at the crime scene and mixed them with the samples of other trees before handing all the samples to the geneticist.

It was found that all samples had a distinct DNA profile, but the profile of one of the samples matched the profile of the pod taken from the tree at the crime scene, which worried the geneticist a little before he was told about the little trick the investigators had played. The results re-assured the investigators that their forensic evidence could stand judicial scrutiny.
Police took Mark Bogan into custody, and he was charged with the murder of Denise Johnson. However, when the case reached the court, the hearing was first held before a judge and for three days lawyers and experts went back and forth over whether plant DNA could be admitted as valid forensic evidence in a criminal trial because it had never been done before anywhere in the world. All scientists agreed that plant DNA, much like human DNA, was unique to individual plants. DNA evidence was thus allowed to be admitted as evidence in the trial, and it became the first case in the world in which a plant DNA was entered as valid forensic evidence.

The jury trial began. According to the prosecution’s story before the jury, Bogan met Denise at the phone booth and she asked him to give her a ride, like Bogan had told the police. They then went to a deserted place to have consensual sex. Bogan asked Denise to try some light bondage, to which Denise agreed. Bogan used some wires and shoelaces to tie her wrists and ankles. Bogan’s ex-girlfriends testified that Bogan was into bondage.

However, after playing along for a while, Denise objected to what Bogan was doing to her and asked him to stop. When he did not pay heed, she pushed him away and got out of the car and tried to run. Bogan chased her and dragged her to the ground before strangling her with her own t-shirt in anger, after which he dropped the body into the bushes and left. While he was driving away from the crime scene, his truck grazed the Palo Verde tree and the two bean pods fell into the back of the truck.

A witness testified that he saw a truck of the kind and make driven by Mark Bogan coming from the side of the crime scene at about 1:30 a.m. on the night Denise was killed. Bogan lived at a driving distance of 18 minutes from the crime scene and his wife told the police that she woke up as Bogan drove in a little after 2:00 a.m. that night, which was consistent with the story of the prosecution and also lined up neatly with the account of the witness who saw Bogan exit the area around the crime scene. However, the body of evidence was largely circumstantial except the DNA profile of the Palo Verde pods found in Bogan’s truck, which sealed his fate.

The defence could not assail the science involved in the DNA evidence produced by the prosecution. So, they chose to do the next best thing – attack the evidence itself. The defence argued that the pods were planted. But it was shown that the pods were collected from Bogan’s truck and stored as evidence before the samples were taken and sent for the DNA test. In fact, the pods could not have been planted because at the time they were picked from the truck, they did not seem to have any connection with the crime. The connection emerged later. Thus, the argument advanced by the defence fell flat.

The jury found Mark Bogan guilty of murder in the first degree and sentenced him to life imprisonment without the possibility of parole for 25 years. The verdict was challenged in appeal before the appellate court, which upheld the conviction as well as the sentence. Mark Bogan maintains his innocence. However, his conviction has the distinction of being the first in the world to be based on plant DNA.

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