The Last Straw (37 page)

“Now, you are only interested in a small piece of the DNA. To identify this piece of DNA you need to add two short pieces of artificially made DNA — maybe twenty or thirty base pairs in length — called primers that will match the DNA sequences either side of the bit you are interested in. It’s a bit like putting brackets around the word you are interested in in a sentence. To do this you cool the solution down to between forty-five degrees Celsius and sixty-five degrees Celsius for about forty-five seconds, which allows this primer DNA to join the matching sequences of the original template DNA.

“Now comes the clever bit. If you raise the temperature to about seventy-two degrees Celsius, an enzyme called a polymerase builds up the missing half of the ladder using raw chemicals that you added to the solution at the start. Depending on what type of polymerase enzyme you use, a good rule of thumb is that it takes about one minute to make a thousand base pairs of DNA. The result is that where you started off with a single very long ladder of DNA, most of which you don’t want, you now have two short DNA ladders, only containing the DNA sequence you are interested in.

“But it doesn’t stop there. If you repeat the cycle, you will use the new ladders as a template also, so those two molecules become four. Repeat again and the four become eight. Then sixteen, thirty-two, sixty-four, one hundred twenty-eight…”

Warren whistled. “The power of powers, eh? So after all that, give me a figure, Karen. How long do you think this PCR reaction would have taken, assuming that he completed it?”

Karen looked uncomfortable, nervously shuffling her notes. “There is a lot of guesswork here and I’m using figures from my own reactions, which might be completely different from anything he is using, but if we assume that he does thirty cycles, with an extension time of one minute — assuming he is amplifying one thousand base pairs — then by the time he’s added on another four minutes at the end to finish off any uncompleted reactions, I’m calculating eighty-four minutes, not including the time taken to actually set up the machine and retrieve his samples at the end of the run.”

Warren looked at her figures thoughtfully for a few long moments, before scribbling a few numbers of his own. Karen forced herself to breathe normally.

“You realise that if he did an extension time of only half a minute, he would only need about seventy minutes. Same thing if he kept it at one minute but only did twenty-five cycles. That’s getting pretty close to the sixty-eight minutes.”

“I know. There is a lot of guesswork involved. I need to get a look at the program he used ideally.”

Warren raised an eyebrow. “Is that possible?”

“I think so, sir. It should be stored in the memory of the PCR machine.”

“All of this is pretty circumstantial, you realise? It’s interesting, but not conclusive.”

Karen nodded, unable to say anything.

“Good, just so you understand.” He stood up. “Nice thinking, Karen. After my conversation with DI Sutton last night, it was decided that another look at that PCR room is on the cards — you’ve just bumped that up to our number one priority.”

Chapter 39

Much to Karen’s surprise, Jones’ first act was to call in DI Tony Sutton. Her first impression of him that morning had been correct: he looked decidedly dishevelled. Jones filled in Sutton with an abridged version of what Karen had just told him. Sutton thought for a few moments, before nodding his head slowly. “Still doesn’t let Severino off the hook, but it’s definitely food for thought.” He turned to Karen. “Nice thinking, Detective. That insider knowledge is something that a couple of old plods like DCI Jones and me lack. You get any more good ideas, you make sure that you share them with us.”

Karen nodded, unable to speak. To her chagrin, she could feel her cheeks turning pink. Neither man seemed to notice, however, as they bantered in a way that she hadn’t witnessed before. “I don’t mind being called a plod, Tony, but a little less of the old, please.”

* * *

After a few quick phone calls to arrange for someone at the university to meet them and for a forensics team from Welwyn to provide support, the three officers clambered into Jones’ dark blue Ford Mondeo. As they pulled out of the car park Karen noticed that Sutton also appeared to be wearing rather a lot of cologne. Sitting behind him, she got a full dose blown over her by the car’s air conditioning. Karen could also smell what seemed like the faintest whiff of stale beer mingling slightly with the cologne. It didn’t take a fully trained detective to work out what had happened the previous day. Although two senior officers getting drunk whilst in the middle of an ongoing case seemed a bit unprofessional to Karen, after work or not, she couldn’t deny that it seemed to have cleared the air somewhat. The atmosphere between the two men had been almost toxic the day before, yet now seemed far more comfortable. Well, as long as it got the job done, she decided.

Pulling into the increasingly familiar car park to the Biology department, Karen noticed that there were far more cars present.

“The building reopened yesterday,” Jones explained. “The end of the corridor with Tunbridge’s lab is still taped off as a crime scene although it’ll have to reopen soon. Forensics are pretty much done so we can’t justify keeping it closed much longer.”

Sutton scowled slightly. “Let’s hope that we haven’t lost any evidence in the past twenty-four hours.”

Sitting in the back seat, Karen felt a slight stab of shame. She’d visited the PCR room Saturday morning, but it had taken her until last night to notice any potential discrepancies in Spencer’s account. Sutton was right: who knew what evidence had been destroyed in the meantime?

Exiting the car, the three police officers headed in through the entrance. Jones showed his badge to the receptionist, who had been told to expect them. By the time the three officers had signed the visitors’ log and each been given a badge on a lanyard, a soft-spoken young woman had arrived to greet them. When she introduced herself as Candice Gardner, Warren was slightly disappointed to learn that she was Professor Tompkinson’s personal assistant. For some reason, when seeing her name plate on her desk on Saturday he had pictured Mrs Gardner as a late-middle aged woman, dressed in a voluminous flowery dress, peering over half-moon spectacles disdainfully at anyone wishing to disturb the revered professor. Warren had lost count of the number of stereotypes he’d had shattered over the past few days.

As they walked through the main administration office it was obvious that the department was operating at full capacity again. When Warren commented upon this, Gardner smiled tightly. “We’ve been closed for three days. It was the last thing we needed the week that the A level results came out and clearing for university places started.” Her tone almost made Warren want to apologise on behalf of Tunbridge and his murderer for the inconvenience. He exchanged a glance with Sutton, who raised an eyebrow, clearly thinking something similar.

The three officers entered Tompkinson’s office, Warren introducing Tony Sutton, who had not yet met the professor. He remained seated, his hands shaking slightly. He looked exhausted, Warren noted.

“Forgive my manners. I’m having a bit of a flare up today.” As he said so his head bobbed backward and forward like a hen pecking for grubs. His voice was reedy and Jones noted a faint slur to the ‘S’ at the end of ‘manners’.

“Not at all, Professor. I hope not to keep you too long, I realise that this is a busy time of the year for you.”

Tompkinson waved vaguely at a large pile of paper on the edge of the desk. “I’ve been trying to work out what to do with Alan’s research group over the next few weeks. The funeral is next Monday, I believe, and we hope to be up and running again by the middle of next week — assuming that you have finished your investigation now?”

“Well, as you know, we have charged somebody with the crime. Now it’s just a case of clearing up a few loose ends,” Warren said carefully. Instinctively, he was unwilling to suggest that the investigation was still open, feeling it best to keep his cards close to his chest.

Apparently satisfied with the vagueness of the answer, Tompkinson gestured to Warren to go ahead with his request.

“We’d like another quick look at the PCR room, if you don’t mind.”

“Of course. I must admit I don’t really spend much time there myself and wouldn’t really know how to drive most of the equipment in there even if I did, but I can probably show you around. It’s a shame that Mark Crawley isn’t here today. He helped design and equip the room a few years ago.” He chuckled slightly. “Alan was not impressed. Maggie Gwyer was supposed to be designing the room, but she broke her leg in a skiing accident and Mark had to take over. He spent rather more time on the project than Alan felt appropriate — probably glad of the opportunity to work away from the boss for a change.”

“Where is Dr Crawley today?” Warren asked smoothly.

“He’s at home with a migraine, poor man. It came on yesterday. He suddenly went as white as a sheet and had to be excused from our meeting.” Tompkinson’s gaze became sympathetic. “To be honest I’m amazed it took this long. The stress must have been intolerable for the poor man.”

Warren clucked his tongue sympathetically, before suggesting that they move on.

“So what is it you are looking for?” asked Tompkinson as he led them down the corridor to the small room. His walk was slow, almost shuffling, Warren observed. Assuming that the man wasn’t a great actor, Warren felt confident that their initial feeling that he couldn’t have been the killer was correct. It didn’t mean he couldn’t be involved in other ways, of course, Jones cautioned himself.

“Like I said, just a few loose ends we need to tie up. Dot the Is, cross the Ts,” Warren replied nonchalantly, repeating the cliché again.

Stopping at the door, Warren saw that the sticky blue and white striped crime-scene tape was still across the door. Slitting it easily with his keys, he stepped to one side whilst Tompkinson swiped his card through the lock. With a metallic click, the door unlocked and the familiar blast of icy cold air rushed out. The three officers exchanged quick glances, all of them thinking the same thing: that stepping into this room on a hot August evening wearing nothing but a T-shirt and thin lab coat would be uncomfortable to say the least. Spending over an hour in the room would be downright unpleasant.

The room, of course, was just how they had left it and so Karen went straight to the black PCR machine. Double-checking the sign-up sheet, she confirmed that it was indeed this machine that Spencer had booked to use Friday night.

Tompkinson moved next to her. “What are you looking for?” he enquired.

“I want to see what the last program run on this machine was.”

Tompkinson looked at her curiously. “Why do you need to know?”

“Just dotting those Is and crossing those Ts,” interjected Jones. “Would you be able to retrieve that information?”

“Sorry, Detective, I wouldn’t have the faintest idea. By the time these PCR machines were all the rage, most of the bench-work in my laboratory was being done by my grad students and postdocs. I understand the theory, of course, but I couldn’t operate one of these things.”

“Oh, hang on, this might help.” Karen plucked an A4 folder off the shelf above the machine. “If in doubt, read the instruction manual, as my dad is so fond of saying. This’ll tell us if the machine saves the last program used.” She started leafing through the manual quickly. “Here it is. May I?” The question was aimed at Warren, who simply handed her some latex gloves.

“Are you sure you know what you are doing? That’s a very expensive piece of equipment,” asked Tompkinson, looking rather uncomfortable.

“No problem. I ran loads of PCR reactions when I was at university on a machine very similar to this.”

Warren hid his smile; the young detective was quite feisty when she got going. Her personnel file had claimed that she was tenacious and not easily dissuaded when she felt she was on the right track. He had a feeling that she would go far in CID.

At his nod, the young detective started pressing buttons. Immediately the front panel and several LEDs lit up and a fan started whirring loudly. The small screen proclaimed it was running a diagnostic.

At a glance from Warren, Tony spoke up for the first time since entering the room. “This is a pretty impressive room, Professor Tompkinson. I have to admit that science wasn’t my strong suit at school. I don’t have a clue what any of this stuff does.”

Turning to the burly detective, Tompkinson smiled. “Of course, I forgot that you didn’t come in here on Saturday.”

As Sutton continued to pepper Tompkinson with questions Warren focused his attention on the PCR machine. The start-up procedure was clearly finished and Karen pressed a few more keys. The screen switched to a list of cryptic names next to what appeared to be dates. The title at the top of the screen read ‘User Log file’. Directly below that ‘TOM1 Started 2107 8/12/11 Completed’.

“If I’m reading this right, the program TOM1 was run Friday night a few minutes after Spencer swiped into the room,” said Karen, quietly.

“Can you see how long this program TOM1 would have run for?”

Pressing a few more keys, Karen called up the stored program list. The screen was arranged rather like a simple PC’s file manager with folders on the left and programs contained within those folders on the right. Selecting a folder labelled TOM revealed a half-dozen programs, numbered sequentially. Karen selected TOM1 and ‘view’. The screen immediately filled with what looked like a basic computer program. Even to Warren’s untrained eye, he could see each step of the program clearly. Karen pulled out her notepad and started jotting down numbers.

300s activate

45s melt

45s anneal

120s extension

30 cycles

300s final extension.

Shutdown

Even without doing the maths, Warren could see that the program would run for considerably longer than the sixty-eight minutes that Spencer was in the room.

“This is weird,” whispered Karen. “The last command told the machine to shut down, rather than hold the samples at four degrees Celsius until he fetched them. DNA is fairly robust, but it’s good practice to keep your samples cool or even freeze them until you need them.” She lifted each of the four hinged lids, revealing empty slots.