“Simon reckoned the killer might want to try and observe police response at close range, having taken such care over his gruesome death installation,” said Gibbs. “For the benefit of an audience, presumably—so he wouldn’t want to miss out on seeing how that audience reacted.”

“Makes sense,” said Charlie.

“Anyway, at ten fifty-five, the Audi driver would have found herself crawling forward in slow-moving traffic, delayed by police in the road ahead—police she’d have been able to see stopping and talking to other drivers—but she’d also have been able to see that the delay wasn’t severe. Wherever she wanted to go beyond Elmhirst Road, she’d have been quicker waiting than doubling back and taking a different route. And no one else waiting in the line did a U-turn. Not one single other driver.”

“I refer you once again to my birthday-card-delivery scenario,” said Charlie.

“Except look at this,” said Sellers. “Same camera fifty minutes later. The same silver Audi drives along Lupton Road coming from the Silsford direction, heading south this time. It doesn’t turn into Elmhirst, but look . . . see how it slows almost to a standstill as it passes the junction?”

It was undeniable.

“The driver wanted to see if the police were still there,” said Gibbs. “Why else would she have slowed down as she approached the junction? And why does she care what the police are up to?”

“Nosiness?” Charlie suggested. “Most people like to have a gawk if they think something excitingly horrible’s going on. We’re all ghouls at heart.”

“Would most people be nosey enough, and have the spare time, to come back to the same place twice in one day to gawk?” Gibbs asked. “Also, if she wanted to know what was going on, why didn’t she stay in the slow-moving traffic, let the police stop her when it was her turn and just ask them what was happening?”

“OK, so we fast-forward again . . .” said Sellers, “to . . . here.” He pointed the remote control at the screen and pressed “play.” “Forty minutes later, she’s back, other side of the road, going north again. This time, she comes to a complete stop on Lupton Road at the exact point that’d give her the best view up Elmhirst, holding up the cars behind her.”

“O . . . K,” said Charlie. “So she’s very, very nosey.”

“And then we fast-forward again and find . . .”

“She comes back again?”

“An hour and five minutes later, yeah,” said Gibbs.

He, Charlie and Sellers watched in silence as the Audi on the screen drove southbound along Lupton Road and started to brake as it neared the junction with Elmhirst.

“Again, she stops and sits at the end of Lupton, blocking the traffic,” said Sellers. “For even longer this time. Look at the line behind her—can’t you just hear the beeping of all those angry horns? Still, she stays put for a full minute.”