‘The footprints bother me,’ Sara said. ‘Why would her feet be bloody by the time she gets up the stairs?’

‘No shoes?’ Charlie guessed. ‘There’s a ton of broken glass down there, some of it covered with blood. Which reminds me, we found a small amount of dried blood on the floor downstairs. Looks like a bad nosebleed.’

‘That could fit with the drug paraphernalia, but we should take a sample anyway.’

‘Excuse me, sir.’ Gary, the cat-rescuing tech, walked up behind Charlie. ‘I couldn’t help but overhearing, and I was wondering about the struggle for the gun. Like, if she was twisted on her side when they struggled on the stairs, wouldn’t the muzzle of the gun be pointing up, more toward the ceiling?’ He tried to approximate the pose, hands in the air like Farrah Fawcett in a TV show that had been off the air for years before he was born.

‘More like this,’ Charlie said, striking his own pose. ‘And then the gun could turn this way . . .’ He tilted his hand. ‘I look like a Heisman Trophy, don’t I?’

Sara’s laugh was more genuine this time, because they both looked ridiculous. ‘Maybe we should get the computer geeks in here.’

Gary picked up a tray of vials. ‘I took samples from everywhere I saw blood. I also swabbed the trickle of blood on Harding’s neck. Dr Linton, do you mind if I watch you type the blood? I’ve never seen it done before.’

Sara suddenly felt ancient. Forget Farrah Fawcett. Gary had likely been in diapers when O.J. Simpson’s lawyers had educated America about DNA. ‘I’d be happy to.’

Gary practically skipped down the stairs. Sara followed at a more careful pace. She tried not to think about earlier when she’d glanced over at Will working the scissor lift. The funny way he’d seethed at Collier for checking her out, as if Sara would ever give another man the time of day.

She asked Gary, ‘What do you know about blood types?’

‘There are four main groups,’ he answered. ‘A, B, AB and O.’

‘Correct. For the most part, all humans belong to one of those groups, which are based on genetically determined antigens that attach to red blood cells. The ABO test determines whether or not the antigen is present by using a reagent that agglutinates when it comes into contact with the blood.’

‘Yes, ma’am.’ Gary looked lost. ‘Thank you.’

She tried again. ‘You basically drop blood on a pre-prepared card, mix it around, and it tells you what the type is.’

‘Oh.’ He took the clipboard from the cop standing inside the doorway and signed out. ‘That’s cool.’

He opened the door. Sara was blinded by a blast of sunlight, so she couldn’t tell if Gary was really interested or just being polite. She scribbled her signature below his. Her eyes took their time adjusting as they walked across the parking lot. Gary took off his hairnet and tightened the band around his ponytail. He had already unzipped his Tyvek suit. His navy-blue GBI T-shirt had the sleeves tightly rolled up to his shoulders. More tattoos covered his arms. He wore a thick gold necklace with a medallion that caught the sunlight like a mirror.

She glanced around the parking lot and adjacent buildings, telling herself that she wasn’t looking for Will or even Amanda, but still feeling disappointed when she didn’t find either. Sara looked down at her phone to see if Amanda had sent her Angie’s blood type. She hadn’t yet, which was strange. Amanda was usually quick. Sara touched her finger to the phone icon. This would be a legitimate reason to call. She could ask Amanda about Angie’s records and then casually question whether there was anything else going on, like had Will found Angie and carried her in his arms all the way to the hospital.

Sara returned her phone to her pocket.

She looked up, then quickly back down again. The sun was shining straight into her eyes. She guessed it was around ten o’clock, if she was remembering her Girl Scout training. The sunlight was so unrelenting that it brought tears into her eyes. She had to keep her gaze down as she made her way past Harding’s burned-out Kia. The car was being thoroughly examined by two techs who were on their knees with magnifying glasses. The blackened frame had only slightly cooled down. Sara could still feel the heat radiating off the metal as she walked by.

The GBI’s Department of Forensic Sciences mobile lab had been created inside a limousine bus that had been confiscated from a guy running a Medicare fraud. The seating had been torn out to accommodate a long desk with banks of computers and storage for various collection kits and evidence bags. Most importantly, the air conditioning had been left intact. Sara almost fell to her knees in relief when the cool air touched her skin.

Gary put the tray of samples down on the desk. He pulled out a chair for Sara, then took his own. She tried not to stare at his necklace. The medallion read SLAM.

He asked, ‘Can you tell sex or race with the kit?’

She used a paper towel to wipe the sweat off her neck and face. ‘With sex, you’d need a DNA test for the presence or absence of a Y chromosome.’ She started searching the cubbies and drawers for the familiar EldonCard typing kits that she had ordered off Amazon because they were cheaper than the local supplier. ‘For race, you can fall back on statistics, but it’s not at all definitive. Caucasians have a relatively high number of As. Hispanics have a high number of Os. Asians and African Americans have a high number of Bs.’

‘What about people who are mixed race?’

She wondered if he was asking the question because of Angie. She had Mediterranean features—olive skin and luxuriant brown hair and a curvaceous figure. The only time Sara had stood beside Angie, she’d felt like the proverbial gawky, redheaded stepchild.

She told Gary, ‘Mixed race is a bit more complicated. Parents don’t always match their children’s blood type, but their alleles dictate the blood type. Two parents, type AB and type O, can have a child type A or B, but not O or AB. Two Os can only have an O, but nothing else.’

‘Wow.’ Gary scratched his goatee. ‘Most of the stuff they taught us about blood in school had to do with DNA. Collecting, processing. This is blowing my mind.’

Sara wasn’t sure whether or not he was being genuine. Nerds had it so much easier now. At Gary’s age, she’d stuck out like a sore distal phalange.

She offered, ‘I’ll do the first typing. You’ll do the second. I’ll make sure you have the hang of it and then you can do the others.’

‘Cool.’ He flashed a smile. ‘Thank you, Dr Linton.’

‘Sara.’ She sliced open the metal foil around the EldonCard. ‘This is the test card.’ She showed him the white index card with black print. At the top were four empty circles, or wells, each with a dot of reagent at their center. Beneath the circles were labels: ANTI-A, ANTI-B, ANTI-D, and a control.

‘Anti-D?’ Gary asked.

‘D tests for the Rh factor.’ Sara spared him another long lecture. ‘The absence or presence of rhesus gives you the positive or the negative after the blood type. So, if you see blood clotting in the A circle and blood clotting in the D, that means your blood type is A-positive. If there’s no clotting in the D, then it’s A-negative.’

‘Rhesus?’