The Perfect Alibi (Robin Lockwood #2)(42)
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Kellerman had suggested meeting at Patty’s Cafe, a locally owned coffeehouse on the outskirts of downtown. Ten minutes after he sat down in a booth in the back, a thin young man with sandy hair walked in. The man halted at the entrance and looked around.
Kellerman raised a hand, and the man walked to the booth. “Thanks for coming, Mr. Nilson.”
“It’s Doctor, actually.”
“Sorry,” Kellerman apologized. “What’s your field?”
“Computer science, but I’ve studied biology and genetics.”
“Impressive. When did you start your company?”
“Seven months ago. I spent a few years in the crime lab in Cleveland, Ohio, and decided to move to Portland to provide forensic services.”
Kellerman sensed that he was hearing a sales pitch. “How’s it going?”
Nilson smiled. “Slow, like most start-ups. That’s why I was excited when Mr. Okonjo called. This gives us a chance to get our name out there.”
Kellerman had done some research on Nilson Forensics and its owner in the time between taking Nilson’s call and coming to this meeting. He knew that Nilson had sunk his life savings into the business and that he was shy on customers to the point where he might have to declare bankruptcy.
“Dr. Nilson, can you explain what your lab does that the Oregon State Crime Lab can’t do? And please remember that I’m an idiot when it comes to science.”
“How much do you know about DNA?”
“It’s come up in other cases, but I’m no expert.”
“Let’s start with the basics: DNA is a molecule containing genetic material that codes for the unique physical characteristics of human beings. DNA is composed of four chemicals called nucleotides, or bases. The shorthand for them are A, C, G, and T. These bases pair together in the following way: A with T, and C with G. These pairs repeat in varying lengths and form rungs on the double helix that constitutes the DNA molecule.
“Now, the double helix is wound very tightly into a chromosome. A gene refers to a sequence of base pairs along a given portion of the DNA double helix which code for a certain trait, like blue eyes. Different genes are located in different places along a chromosome.
“An allele is one of several alternative forms of a gene that occurs in the same position on a specific chromosome. In other words, an allele is a variation in the number of times the base pairs of DNA repeat at a particular location on a particular chromosome. This number of repeats varies among humans. Modern forensic analysis focuses on the number of times the base pairs repeat at a variety of spots along a person’s chromosomes. By measuring and comparing the number of repeats at given locations, an analyst can distinguish one individual from another.”
“Okay, I get that. But what do you do that the crime lab can’t?”
“The normal type of DNA analysis is performed in a laboratory, like the Oregon State Crime Lab,” Nilson said. “DNA is extracted from the evidence, which can be a person’s saliva or a sample of semen or blood. I won’t go into the whole procedure, but you can get a graph of the DNA that can be used for comparison purposes.
“The problem for your crime lab in Mr. Nylander’s case was that the amount of blood found under Nylander’s fingernail was so small that the normal procedures for extracting and analyzing it didn’t work. And that’s where we come in.
“Nilson Forensics has developed a probabilistic genotyping software program. Probabilistic genotyping software uses computer science algorithms to perform complex mathematical and statistical calculations that are designed to calculate likelihood ratios or LRs. LRs reflect the relative probability of a particular finding under alternative theories about its origin. In forensic DNA analysis, the LR can be stated as, ‘The profile is x amount of times more likely if the prosecutor’s hypothesis is true than the defendant’s hypothesis.’ Your hypothesis is that the defendant contributed the sample, and the defendant’s hypothesis is that someone else contributed the sample.”
“So, you make guesses about the probability of the DNA in the blood under Nylander’s fingernail matching the DNA of a particular person?” Kellerman said.
“Exactly.” Nilson beamed like a teacher who has discovered a particularly apt pupil.
“You told me that the DNA in the sample matched Douglas Armstrong’s DNA.”
“Not exactly. There is some indication we have a match, but the probability isn’t high enough for me to make a conclusive statement that the blood came from Mr. Armstrong.”
“That’s too bad,” the prosecutor said. “If you were certain enough to testify that the blood is Armstrong’s, it would give your company a real platform. This case is going to be front-page news. Media coverage is going to be huge.”
Nilson frowned. “Of course, I’d love the publicity, but I can testify only about what the science shows.”
“Certainly, but you said you deal in probabilities, not absolute facts. Is there a chance that a retest would show a different result?”
“I’m not certain what you’re suggesting.”
“I’m not suggesting anything. Like I said, I’m a real dummy when it comes to science. I was just wondering if it would be worth using your software again to see if you can get a more definitive result. My office would compensate you for the extra work, and I’ll certainly spread the word about your business regardless of the outcome of a retest.”