When Plant DNA became a crucial piece of evidence

On May 3, 1992, a motorcyclist came across a woman's dead body in a deserted area on the outskirts of Phoenix in Maricopa County, Arizona. Immediately, he reported the horrible find to the police. The woman apparently had been beaten up, bound, and strangled to death. There was no clothing on the victim's body 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 was probably used to strangle her. What a brutal scenario!

The condition of the body gave a strong suspicion of rape. Her ankles wore shoelaces and a string with which they seemed to be loosely tied. The investigators also found a syringe and a few pieces of clothing around the body. While the investigators were still working on the scene of the crime, they repeatedly heard the beep of the electronic device. They looked around and found a pager lying nearby, their first workable piece of evidence. After the evidence was collected from the scene, the body was sent to the autopsy and victim identification medical examiner. A fingerprint search has been found to match. Denise Johnson, 30, was the victim of a single mother of two children.

Denise was born and raised in Phoenix. But as she grew up, she was drawn to the wrong kind of people, the kind that rarely is- seldom good news. Drugs, alcohol, and partying were a way of life with Denise, who made her live on the street mostly by selling drugs and short-term truck drivers. With Denise’s life in mind, there was a wide range of scenarios that could have landed her where she was found. So, looking at her life, it wasn't easy for the investigators to lead a prime suspect. They looked at the pager and found that it belonged to Mark Bogan, a local truck driver. He was summoned to question.

Bogan told the investigators that he had stopped making a phone call on his way home from work on May 2, 1992, when Denise approached him and asked for an interstate ride. Bogan is obliged to do this. What happened while they were driving? Denise made some sexual overtures that led Bogan to stop the vehicle at a deserted spot and to have consensual sex in the truck cabin. That wasn't the end of it, however. Bogan claimed that while he was dropping her off, she was making a move to steal his stuff from the dashboard, but she was caught in the act. Bogan wrenched his wallet back after a small fight. She walked out of the car and walked away on foot. This is 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'd dropped it somewhere, and he called the pager company to report he’d lost it.

However, during the investigation, the police could not help finding scratch marks on Bogan's side of the face suggesting a physical struggle, and these scratches could leave blood or skin under Denise's nails if the injury was incurred during the scuffle between the two of them. Let’s see what Autopsy Report revealed. The autopsy did not find any tissue or blood under Denise's fingernails. It revealed that Denise was strangled to death and that she was high on cocaine at the time of her death, but there were no signs of sexual activity. There was no blood, no foreign hair, no saliva on her body. It was not raped, as the state of the body had suggested. There was nothing to connect Bogan to the crime, either. By this point, there was little left for the investigators to investigate – no leads and no suspects.

Now the work of Detective starts-

The day after Denise's body was discovered, Homicide Detective Charles Norton, to whom the case had been assigned, visited the crime scene to get familiar with the area where the body had been discovered and to search for signs and clues that the first responders or the crime scene investigators may have overlooked. Detective Norton noticed a fresh abrasion on one of the low branches of the Palo Verde vine. It was very likely that the abrasion on the tree had something to do with the crime, since the area was largely abandoned, and the possibility of human activity was quite small. This could only be a huge irony that the fresh abrasion was triggered by something different and unrelated to Denise’s death at the same time as death. So, the probability of the two items being related was very high. Detective Norton took an image of the abrasion and plucked a few beans out of the tree for further study.

Mark Bogan's truck had been thoroughly tested for evidence. There was no blood, no semen, no saliva, no fingerprints, or anything else that linked Bogan or the truck to the crime. There was no visible proof to indicate that Denise Johnson had entered a truck trip. The police, however, found two bean pods from the Palo Verde tree in the back of the vehicle. The pods have been photographed and preserved as evidence. Did anyone imagine this?

The discovery of bean pods led to the belief that Bogan's truck was rubbing against the Palo Verde tree, leaving an abrasive on the tree and dropping the bean pods into the truck as he was driving away from the scene of the crime. Bogan claimed that he had left Denise on the bridge and had driven away; whereas the body had been discovered far off the bridge and that Bogan could have had no excuse to be on the scene of the crime if he had nothing to do with Denise’s murder. Nonetheless, the claim will only hold up if it could be confirmed that the bean pods found in Bogan's truck came from the Palo Verde tree on the scene of the crime. It wasn't an easy task since there are a decent number of Palo Verde trees in Arizona. It is not for some reason, after all, that on 9 April 1954 the Palo Verde tree was named as the official state tree of Arizona by State legislation to that effect. Therefore, the only choice was to try to match the DNA of the plant, if that was possible.

The next challenge was to- find someone who could do it for them. Therefore, the detective started to approach someone he thought would be able to help him do that. No one had done this before, for sure, and others thought it wasn't possible. Then some felt it could be done, but the costs involved would be enormous. Finally, after recruiting scientists from all over the United States, the detective found help at the University of Arizona. A geneticist has agreed to lend a helping hand. He used a technique called Randomly Amplified Polymorphic DNA (RAPD) technique to match the two sets of plant DNA – one of the pods found in Bogan's truck and the other of the pods examined by the detective. The RAPD test is distinct from the Restriction Fragment Length Polymorphism (RFLP) test, which is used to evaluate and align human DNA.

The DNA testing showed that the pods found in the pick-up truck owned by Mark Bogan came from the tree on the scene of the crime. Nevertheless, because plant DNA had never been used as evidence in a court of law, the prosecutor needed to prove that all Palo Verde trees had a distinct DNA profile and that the pods in Bogan's truck could not have been there by pure coincidence. Samples from a hundred Palo Verde trees in Arizona were collected and sent to the same plant geneticist. To order to make the analysis more complex and vaguer, the police also gathered samples from the Palo Verde tree on the scene of the crime and mixed them with samples from other trees before giving all the samples to the geneticist.

What ultimately was found out-

All the 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 puzzled the geneticist a little before he was told about the little trick the investigators had done. The findings re-assuring the investigators that their forensic evidence will be subject to judicial review. The police arrested Mark Bogan and charged him with the murder of Denise Johnson. However, when the case was brought before the court, the hearing was held for the first time before a judge and for three days lawyers and experts went back and forth on whether plant DNA could be admitted as valid forensic evidence in a criminal trial because it had never been done anywhere in the world. All scientists agreed that plant DNA, like human DNA, is unique to particular plants. DNA evidence was therefore accepted as evidence in the trial and was the first case in the world in which plant DNA was entered as legitimate forensic evidence.

What happened in trail?

The jury trial began. According to the prosecution's story before the jury, Bogan confronted Denise at the phone booth and begged him to give her a ride, as Bogan had told the police. They were going to a desolate place to have consensual sex. Bogan asked Denise to try some light bondage that Denise had agreed to do. Bogan used a few wires and shoes to bind 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 had done to her and begged her to quit. When he didn't pay attention to himself, she kicked him out of the car and tried to run away. Bogan pursued her and pulled her to the ground before strangling her in the rage with her own t-shirt, after which he dropped his body in the bushes and fled. While he was driving away from the scene of the crime, 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 vehicle of the sort carrying Mark Bogan from the side of the crime scene at around 1:30 a.m. was the night Denise was murdered. Bogan lived at a driving distance of 18 minutes from the scene of the crime, and his wife told the police she woke up when Bogan was driving a little after 2:00 a.m. That night, which was consistent with the prosecution's account and also matched exactly the testimony of the witness who saw Bogan flee the area near the scene of the crime. However, the body of proof was mostly circumstantial, except for the DNA profile of the Palo Verde pods found in Bogan’s vehicle, which sealed his fate.

The defense could not assail the science involved in the DNA evidence provided by the prosecution. Therefore, they've decided to do the next best thing – question the proof itself. The prosecution claimed that the seeds had been planted. Nevertheless, it was revealed that the pods were retrieved from the Bogan truck and preserved as evidence until the samples were taken and submitted for DNA testing. In fact, the pods may not have been planted because they did not seem to have any association with the crime at the time they were picked from the truck. Earlier, the link appeared. The argument advanced by the defense, therefore, fell flat.

The jury found Mark Bogan guilty of first-degree murder and sentenced him to life imprisonment for 25 years without the possibility of parole. The decision was appealed to the Supreme Court, which upheld both the conviction and the sentence. Mark Bogan maintained his innocence. His assumption, however, is that he is the first to be founded on plant DNA in the world.