“Yes indeed. But we don’t look at just that one sequence. We look at thirteen
“So how do you deal with that?”
“By increasing the quantity.”
Thursday, 20 August 2009 — 11:30
Martine took the elevator to the fourth level of the parking structure feeling tense and flustered at the amount of time it had taken her to get here. She knew that the trial would have already started, but there was nothing she could do. She just hoped that she could get one of the stringers from the print press to fill her in on anything that she had missed.
There was nothing unusual to alert Martine as the elevator doors opened and she walked over towards her car. Parking structures held no fear for her, at least not in daylight. And there was plenty of daylight seeping in from the periphery to complement the strip lighting.
She pressed her combination on the remote key to open the car, ignoring the man moving things about on the front passenger seat of his aquamarine Mercedes in the adjacent parking spot. At the back of her mind, was the recollection that Elias Claymore’s missing car — like the one used in the rape of Bethel Newton — was the same make and color. And this man was…
She dismissed the thought, opened the driver’s door and slid into her car. She was just about to close the driver’s door when the man standing on the passenger side of the adjacent car lurched at her, shoved her hard into the passenger seat and slammed the door behind him. Before she could scream, he clamped an iron right hand over her mouth, his thumb under her jaw holding it shut. With his free left hand, he operated the mechanism to incline the seat back until it was almost horizontal. Then he started ripping at her clothes.
In those few seconds, terror truly engulfed Martine. They were high up, on the fourth level of the parking structure, so people were less likely to come here than to the lower levels and wouldn’t hear her outside on the street. It was not the beginning or the end of lunch-time so this would not be a key time for people to arrive here or leave. And this man was holding her down, so that she couldn’t be seen by others on this level, even if anybody came. Also he was strong and easily able to withstand her pathetic attempts at resistance.
Her skirt had by this stage been hitched up and her panties and pantyhose ripped off completely. He was now struggling with his own clothes and Martine could feel from the contact between them that he was already aroused physically as well as psychologically. The only thing she didn’t know, as she struggled to reach into her pocket, was whether he intended to let her live when he was finished with her.
Thursday, 20 August 2009 — 11:40
“So Polymerase Chain Reaction is a method of increasing the amount of DNA available for testing?”
Sarah Jensen was continuing her direct examination of Victor Alvarez.
“That’s right.”
“And how does it work?”
Alvarez pressed on the button to show an animation that he could speed up or slow down as he illustrated the process graphically.
“It involves heating and cooling the DNA in a special chamber called a thermal cycler, together with certain other chemicals called enzymes. This causes the DNA to unravel and split into separate strands and then each strand forms a new pair of strands with the other chemicals in the same way as it does in the body, with the bases forming pairs like I said before.”
“And how many times do you do this?”
“It can be anything from twenty-eight cycles to thirty-four. Each cycle doubles the amount of DNA.”
“But once you’ve got enough DNA for testing, how do you distinguish between DNA from the victim and DNA from the perpetrator of the crime?”
“We start off by defining threshold quantities. Anything that shows up in the test in a smaller quantity is simply treated as noise and therefore ignored. Then we look at the relative quantities of what’s left to identify what we call the ‘major contributor’ and the ‘minor contributor’. Next we compare the evidence sample to the victim’s reference sample to determine if the victim is the major or the minor contributor. We do the same with the suspect’s reference sample to see if the suspect matches the other contributor. If we find a sequence in the evidence sample that matches one found in the suspect’s reference sample, then we call that an
“And how many exclusions does it take to exclude a suspect completely?”
“All it takes is
Sarah Jensen paused and turned to the jury, to make sure that this had registered. They set their bar high to include a suspect, and proportionately low to exclude him.
“Now you spoke about the major and the minor contributor. Does that mean that the DNA in the evidence sample is always a mixture?”
“Not always. We can isolate the DNA from sperm using a method called Differential Extraction. We tried that in this case with DNA from a vaginal swab. But unfortunately, in this case, it turned out that there
“And what did that show?”
“The test showed that it contained DNA from Bethel Newton but
“And does exclude Mr Claymore?”
“No, it’s only an exclusion when the evidence sample
“But how do you explain it the absence of any DNA from another contributor?”
“Well, in itself it’s consistent with two explanations. One is the absence of sexual activity. The other is use of a condom.”
“So what did you do then?”
“We then turned our attention to the nail clipping samples from when Miss Newton scratched the victim.”
Thursday, 20 August 2009 — 11:45
Martine was gasping for breath now, struggling against the man’s weight upon her. He had now unfastened his belt and pants and for a brief, fleeting moment he lifted his weight off her so that he could pull them down. It gave her the chance she needed. Quick as a flash, she twisted her body and pulled out the small pepper spray canister. She knew, from her limited training, not to waste any time or effort trying to carefully position the canister. That would merely telegraph her intentions. She swung it close to his face, closed her eyes, held her breath and let
