‘Charlie?’ she called.

He poked his head out of one of the rooms. ‘Yes?’

‘Can you come over here with your camera and some tweezers?’

‘That’s the most interesting proposition I’ve had all week.’ He went back into the room and came out with his camera in one hand and a CSU kit in the other.

Sara pointed to the unicorn’s eye. ‘Here.’

Charlie shuddered. ‘Two things that have always freaked me out: unicorns and eyeballs.’ He took a magnifying glass from the kit and leaned in for a better look. ‘Oh, I see. Excellent catch.’

Sara stood by while Charlie photographed the pierced eye, using a small metal ruler to capture scale. He did the same with the dust below the unicorn, then changed lenses to get a wider view. When he’d finally documented the creature, he handed Sara a pair of needle-nose tweezers. ‘You do the honors.’

Sara was mindful that she could do a lot more harm than good if she didn’t take her time. She was also mindful that she had never lost a game of Operation. She rested the heel of her hand just below the unicorn’s eye. She opened the tweezers just wide enough to still clear the sides of the hole in the iris. Slowly she inserted the blades until she felt something solid. Instead of opening the tweezers, she narrowed them, fairly certain that there would be something to grip. She was right. The tip of the blades caught the flattened rim of what turned out to be a hollow-point bullet.

Charlie said, ‘They shoot unicorns, don’t they?’

Sara smiled. ‘Thirty-eight special?’

‘Looks like it.’ Charlie told her, ‘The G43 was unfired. The clip and chamber had nine-mill American Eagle, full metal jackets.’ Charlie’s mustache twisted to the side in thought. ‘This could be from a revolver.’

‘Could be,’ Sara agreed. A cop of Dale Harding’s age might prefer a revolver to a nine-millimeter. ‘You haven’t found another gun?’

‘Maybe it melted in his car. I’ll let the techs know to look for it.’

Sara sniffed the spent cartridge, picking up the lingering odors of sawdust, graphite and nitroglycerine. ‘Smells recent.’

Charlie took a sniff. ‘I think so. No blood, though.’

‘The bullet would’ve been hot enough to cauterize any bleeding as it went through the body, but there could be microscopic traces.’

‘Kastle-Meyer?’

Sara shook her head. The field blood test was known for false positives. ‘We should let the lab do a wash. I’d hate to be told we used the only viable sample and they can’t test for DNA.’

‘Excellent point.’ Charlie looked down at the floor. ‘I’m no doctor, but if the bullet hit anything big, like an artery, we’d be able to see blood somewhere in this area.’

‘Agreed.’ Sara found a small plastic evidence bag in the CSU kit. Charlie took over the labeling because his handwriting was better.

He said, ‘Just so you know, Amanda authorized rushes on everything, including the DNA.’

‘Twenty-four hours is better than two months.’ Sara studied the bullet hole in the unicorn’s eye. ‘Does this hole look more oval to you?’

‘I saw that when I was taking pictures. We’ll call in the computer geeks to do a rendering, calculate the trajectory, velocity, angles. I’ll let them know about the rush. We should have something back in a few days.’

Sara took a Sharpie pen out of the CSU kit and slid it into the hole. The clipped cap pointed back toward the balcony at a slight angle. ‘Do you have two levels and some string?’

Charlie laughed. ‘You’re a regular MacGyver.’

Sara waited for Charlie to retrieve a ball of string from one of the duffel bags. He tied it to the end of the Sharpie. He took his phone out of his pocket and pulled up a spirit level app.

‘Oh, good thinking.’ Sara pulled out her iPhone. She thumbed through her apps until she found the level. ‘The other side of the balcony is how many yards?’

‘Twenty-eight.’

Sara said, ‘An airborne projectile is subject to the forces of air resistance, wind and gravity.’

‘No wind inside of here. Resistance would be negligible at this distance.’

‘Which leaves gravity.’ Sara placed her phone on top of the Sharpie. The app showed an old-fashioned Stanley level with a digital number below the bubble. ‘I’ve got seven-point-six degrees.’ She placed the phone against the side of the pen for the second reading. The number kept jumping up and down. ‘Let’s call it thirty-two.’

‘Fantastic.’ Charlie started walking backward, rolling out the string, keeping the line tight. Occasionally he stopped and checked the level on his phone against the top and side of the string to make sure he was still on target. As long as he kept the angles consistent, the string would roughly indicate the point at which the bullet had left the muzzle of the gun.

Charlie glanced behind him as he walked, stepping around yellow plastic markers. His hand was too high to reasonably assume an average person had held a gun and fired it from that level. He passed the murder room, the stacked drywall. His hand started to move lower. He didn’t stop until he was at the top of the stairs.

‘Wait.’ Sara looked at the level on her phone. ‘You’re pulling way left.’

‘I have a theory.’ Charlie went down one stair, then another. He looked back at Sara. The hand holding the ball of string went lower, then lower still. Sara kept the pen steady. The string had moved away from the balcony, tensing in the open air like a tightrope, until Charlie’s hand was at his ankle. He used the level to make an adjustment. His hand slid back until it was pressed against the wall. He checked the angles one last time. ‘This is the end of the line, as it were.’

Sara studied the path of the string. Charlie’s theory was as good as any. Whoever had fired the gun would’ve been standing somewhere on the stairs. Or not standing. Charlie’s hand was low, about three inches away from the tread. Two stairs down was the impact point where the woman—likely Angie—had hit the back of her head.

Sara said, ‘They struggled for the gun there.’

‘Angie and Harding.’ Charlie picked up her train of thought. ‘Angie has a gun. She’s running up the stairs. Harding grabs her, bangs the back of her head against the tread. She sees tweety birds. He reaches for the gun. Maybe he bangs the back of her hand into the concrete and she squeezes off a shot.’

‘Angie is right-handed.’ Sara hated that she knew this. ‘If she was on her back, for your theory to work, the gun would have to be in her left hand, which means the bullet would be on that side of the stairs, not here.’

‘She could’ve twisted to her side?’

Sara shrugged, because there weren’t a lot of absolutes considering they were using a ball of string and a free app.

‘Let’s think about this.’ Charlie started rolling up the string. ‘Angie is running away from Harding, revolver in her hand because her Glock somehow got jammed out in the parking lot. She’s almost at the top of the stairs. Harding catches her. The gun goes off. Angie gets away. She goes to the room. Shuts the door. To be continued.’ He held up his finger. ‘Problem is, how would the gun go off? A cop wouldn’t have her finger on the trigger while she ran up the stairs. They’re trained out the wazoo that you rest your finger on the guard until you’re ready to shoot. You don’t unlearn that when you take off your badge.’