Kirsty Mockett met him in the narrow hallway of the cramped house, and showed him a couple of close-up photographs of bloodstains while he climbed into his protective gear. She then led him up the narrow stairs to the landing. The upper floor was cluttered with books, clothing and clerical paraphernalia. She led him into the second bedroom, little more than a low-ceilinged box room. The light was on and the curtains drawn. It had three crammed bookcases, but had been turned into a makeshift gym. A rubber exercise mat occupied much of the floor. Beyond it, a weight training stand was full of dumbbells and free weights.

‘This is what I spotted,’ Kirsty said, kneeling in front of a wooden bookcase, bulging with hardbacks. There was what looked like a small paint run on the spine of one book, no bigger than a map pin and close to the skirting board. ‘It looks like paint, but it’s blood.’

Gillard crouched to look closely. ‘I’m impressed you spotted that.’

Kirsty led him back to the doorway, and flipped off the light switch. Low down on one wall of the darkened room, just above a plug socket, was a spray of iridescent blue measles. The specks continued across a bookcase.

‘BlueStar has done a good job here,’ Gillard said.

‘There’s a directional sweep, as you can see,’ Kirsty said. ‘An arc from left to right, going towards the window, low across the bookcase. There are some runs down onto the skirting board too.’

‘A cut artery, and a surge of blood. That fits with the injuries sustained by the victim. A knife wound to the neck, while he was prone.’

‘It seems to me, sir, that we’ve found the site of the murder.’

Gillard nodded. ‘And someone cleaned up, but not very well.’

‘BlueStar is amazing. You can scrub and scrub with bleach and disinfectant, yet still get a reaction from the solvent. I sprayed this just forty-five minutes ago, and it tells us so much.’

‘Rev Cleaver may have thought he cleaned up well enough. He probably replaced the original carpet, because there’s not a single speck on this one,’ Gillard said.

‘It’s not on most of the books either. What if the killing took place before his tenancy?’

‘Maybe we can establish that,’ Gillard said. He crouched down to look at the bottom row of books again. The blood run she had pointed out earlier stood out in kingfisher blue. ‘If these are Cleaver’s books, brought in with him, then this one drop of blood will prove the killing took place after his tenancy began.’

Looking over the bookcase, neither Gillard nor Kirsty could see any other drops of blood on other books, yet there were dozens of pinpricks of blue light from the edge of the shelves.

‘It looks like most of the books were put here afterwards,’ Kirsty said. ‘You’d expect more contamination on them otherwise.’