In 1989, the murder of a 14 year old girl when he was on his way to school in Las Vegas he shocked the whole city. He appeared the day after leaving home, with clear signs of violence. She had been sexually assaulted and later strangled. Police found traces of the killer’s semen on his shirt. It could be the clue they needed to identify him. However, they only managed to obtain 15 cells and, from them, isolate 0.12 nanograms of DNA.
Even today this is an extremely small sample, making it even smaller in the 1980s, when the forensic genetics he was practically in diapers. Therefore, despite the fact that what was possible was done, the case was ultimately unsolved.
Since then, attempts have been made to identify the killer on two occasions, one in 1998 and one in 2007. However, there were no results. Up to now. And it is that, finally, thanks to an anonymous donation, the murder of the little Stephanie isaacson, has been resolved. And also a record has been broken, since the crime has been solved with the smallest DNA sample in history.
Little DNA to solve a murder
At the dawn of forensic science, the perpetrators of crimes were identified through parameters such as fingerprints or blood group. However, they were very confusing factors, that he could easily target someone who really had nothing to do as the murderer.
Today, however, much more importance is attached to the identification of certain markers in DNA samples. But this has also been a gradual process. In 1985, the geneticist Alec J. Jeffreys developed a technique based on RFLPs, which measure something known as polymorphic length restriction fragments. For this, restriction enzymes were used, proteins that act as pair of scissors, cutting very specific places in the DNA and giving rise to a pattern of fragments that differs from individual to individual. This pattern was known as genetic fingerprint. It was much more specific than what had hitherto been used to identify the perpetrator of a murder or any other crime. However, it had important limitations. For example, they were necessary very large amounts of DNA and it took a long time to do the whole procedure.
For this reason, the introduction in forensic genetics of the PCR it was a breakthrough. It had been designed by Kary Mullis in 1983, but is not yet used in this area. He acted as a kind of molecular photocopier, so that through a very small sample of genetic material, a much larger one could be obtained. The task became much easier and, in addition, gave way to the introduction of new techniques that are even more precise, easier and faster than RFLPs. For example, microsatellites, which are sequences in which a fragment is repeated consecutively. Their distribution can also help identify individuals.
Genetics were taking those first steps when Stephanie’s tragic murder occurred. PCR was already in use, but it was still too small a sample. In fact, even today most commercial tests employ 750-1,000 nanograms of DNA for optimal results, as explained in IFLScience. And in this case they only had 0.12 nanograms. Therefore, although it was possible to obtain a DNA profile to compare it with the FBI databases, there were no results and the case remained unsolved.
The reopening of the case
Today, forensic genetics has come a long way. Very advanced sequencing techniques are used. And also a more specific identification method, based on what are known as SNPs. These are single nucleotide polymorphisms. Or, what is the same, specific variations in one of the building blocks that make up DNA. Or in very few. In recent years, its full potential has been discovered, for example, for the identification of certain diseases. But also in forensic genetics.
For this reason, companies dedicated to the recovery of unsolved cases have emerged, thanks to these more precise techniques. This is, for example, the case of laboratories Othram, in Texas, whose members contacted the Las Vegas Metropolitan Police Department. As explained in an article by The Washington Post, an anonymous donor had offered a large amount of money to fund the resolution of some unsolved Las Vegas case. It didn’t matter which one, the city was the only condition.
Upon receiving the news, the police decided that Stephanie’s murder might be a good option. A) Yes, thanks to new techniques and this funding, in Othram they were able to analyze more deeply the small sample of DNA that they had. They compared it with the profiles of criminals in the area, until they found a safe match with Darren marchand. His genetic profile was on file after he was considered a suspect in the murder of a 24-year-old girl in 1986, when he was only 20. The case was finally dismissed for lack of evidence and he was released. A freedom that allowed him to kill Stephanie three years later.
Unfortunately, it has not been possible to stop him, since the man committed suicide in 1995. But, at least, finally the family of the 14-year-old girl knows who was the soulless one who took her daughter’s life.