David Kessler - No Way Out

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 was no sperm in the sample. We then compared the DNA from another vaginal swab to the reference samples of both Bethel Newton and Elias Claymore.”

“And what did that show?”

“The test showed that it contained DNA from Bethel Newton but not from Mr Claymore or indeed anyone else .”

“And does exclude Mr Claymore?”

“No, it’s only an exclusion when the evidence sample does contain a mixture of DNA from more than one contributor. In this case, all the DNA came from Miss Newton, so that doesn’t eliminate anyone.”

“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.”

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 out a large burst of spray,

The man cried out in agony and anger, twisting away from her onto the driver’s seat and rubbing his eyes — the very thing that one is not supposed to do. Martine herself was gasping and coughing from the back spray. She sat up, to make it harder for him to resume his assault and at the same time grabbed his throat, digging her thumb hard into the soft tissue. He let out another cry of pain, but this time managed to deliver a vicious punch to the side of her face. She was dazed by the force of the punch, but in some way it helped as it made her forget the discomfort of the back spray that was affecting her.

As she recoiled, she grabbed the handle of the front passenger door and tugged at it. Then she remembered that it had a security lock. Fortunately, she knew where everything in the car was. She pressed a button under the dashboard and the passenger door was unlocked. On her second attempt she managed to operate the door mechanism and open the door, but before she could push it wide enough to effect her escape, the man grabbed her arm again. She let out a scream of “fire!” remembering the old rule that people were more likely to respond to the word “fire” than “help.”

He silenced her by placing his hand firmly over her mouth. But it was the same hand that he had used to grab her arm — his other hand was still rubbing his burning eyes. With her arms and hands free, she pushed the passenger door open wider with one hand while using her other — reinforced by a powerful biting action of her teeth — to remove his hand from her mouth. Again he cried out in pain and retracted his hand to suck on the wound and the toothmarks.

Without waiting for him to make another move, she twisted away through the open door and ran out of the car continuing to scream “fire!”

The man knew that there was nothing more he could do to her. He heard the sound of other people coming and realized that he was now in danger. He didn’t know how many people were responding to Martine’s cry, or whether they were security guards or just members of the public. But whoever they were, even if they couldn’t stop him, they would still be witnesses who could identify him.

So he knew he had to flee, and moreover that he had to do so as quickly as possible. He couldn’t start her car as it was one of those modern high-tech ignition systems and he didn’t have the key. She must have put it in her pocket when she reached for the pepper spray. So he leapt out and dived back into his own car via the passenger door, slamming it shut, sliding across the seat and starting the engine as quickly as possible. By the time he had got the engine started there were two security guards charging towards the vehicle, apparently more concerned with stopping him than with helping Martine.

But he knew they wouldn’t shoot. Even if they were armed, they wouldn’t shoot. Their position would be legally precarious if they did. They might have grounds to detain him, but they sure as hell didn’t have grounds to shoot him. They didn’t know that was an attempted rape. For all they knew it could have been a falling out between a pair of lovers or an argument over a parking space. And the word she had shouted that had brought them running was not “rape” but “fire” — hardly grounds to shoot a man.

They tried to run into his path, but he just kept going, sending them spinning out of the way as they dived for cover.

He permitted himself a brief chuckle as he thought about their pathetic and futile effort to stop him. And now he was screeching his way down a series of ramps to get to the exit of the parking structure. A couple of times other cars, in the process of leaving the structure, came perilously close to crossing his path. But the ferocity with which he was driving forced them to hold back or swerve out of the way. So it took him only a minute to get to the exit on 13 thStreet.

But when he got there, in his desperation to escape, he forgot the most basic rule of driving: to look. And a second later, a speeding police car that was answering the call from the security guards, slammed into the left side of the aquamarine Mercedes, sending him reeling.

“The problem with nail clipping samples in cases where the victim scratches the attacker,” said Alvarez, “is that you normally find a large amount of DNA from the victim and only a small amount from the assailant.”

“And can this be resolved by the method you described earlier? Identifying the major and the minor contributor?”

At the defense table, Alex had noticed that Martine wasn’t sitting in the press section. He was idly curious about that but continued to concentrate on the Alvarez testimony.

“Unfortunately that is often impossible, because the sheer volume of DNA from the victim dwarfs the amount of DNA from the other contributor. And if you try to get round this by setting the detection equipment to a more sensitive level, you end up with a lot of background ‘noise’ as we call it.”

“So how do you solve the problem?”

“We turn our attention to a particular type of DNA that comes from the Y chromosome. Only men have a Y chromosome, so that means you’re limiting it to DNA from a man. We’re still looking for repeated sequences — just like with ordinary autosomal DNA — but this time it’s a set of twenty two locations on the Y chomosome.”

He clicked the button and showed an illustration of a strand of Y chromosomal DNA with arrows pointing to various marked sections.

“We use the same processes to break down the DNA into fragments and analyze them and then we get the computer to print out a report showing the length of the sequences at each of the marker locations.”