He wouldn’t normally read this attachment, merely filing it for reference, except that it was flagged up for attention by the lab. Reading through he saw that Jason Waddington’s DNA had turned up in specks of blood on Gillard’s discarded gloves from two crime scenes. One, unsurprisingly, was the Feathers public house fight, where Waddington was punched. The detective had picked up his spectacles and a tooth. But the other was from the Ashtead crime scene.

That must be a mistake.

Gillard didn’t think he had touched Mrs Roy. Lifted the plastic dry-cleaning bag that had been placed over her, yes. But not touched her, so he wouldn’t have touched the hair that was found on her lapel either, nor any markers that Waddington might have left behind. So how did Waddington’s blood get on that glove?

Gillard stroked his chin. There was one horrible possibility that he hardly dared to consider.

When he had finished at the crime scene at the Feathers pub on the Saturday night, he’d tossed the discarded latex gloves and booties into his own discards bin bag before heading off to Ashtead Common. He knew that he had put on fresh gloves and booties when he got there. That was such an ingrained forensic habit he knew he would not have made a mistake. What he could not be sure of was that when he was wearing gloves at Ashtead, either when putting them on or discarding them in the separate bag, he hadn’t touched or gone into the discard bag from the pub fight. Modern DNA techniques were so sensitive that even the tiniest contamination of human blood or sweat could be passed from one glove to another and registered against the wrong crime scene.

Cross-contaminated evidence would be a disaster.

It was always possible, of course, that a junior investigator at CSI had made the mistake, mixing up the two bags of discarded gloves and booties which he had passed across for sending to the lab. Even the lab itself might have made the mistake. There were precedents for each of those errors. Either way, there was a distinct possibility that a huge balls-up had been made, and that Jason Waddington was entirely innocent. He was going to have to let the CPS know, which was embarrassing enough. But what truly terrified him was what Alison Rigby would say.

Gillard sat in the Mount Browne refectory with a big mug of milky coffee and a Danish pastry to mull over the possibilities. He knew that the further down the line this investigation went, the more trouble there would be if Waddington turned out to be innocent. Mixing up the discarded gloves after they were handed in could not in itself have caused a hair from Jason Waddington to end up on Mrs Roy’s coat lapel. Only Gillard’s own mistake could have caused that. He was experienced enough to know that context was everything. The single hair of Jason Waddington’s they’d found on the lapel of Mrs Roy’s coat was no longer a reliable piece of evidence. The mix-up would legally have to be disclosed to the defence, and any half-decent defence lawyer would use it discredit the entire forensic process. That hair might simply have somehow got attached to Gillard’s wrist or jacket cuff, or been floating around the boot when he put on the second pair of gloves. If Waddington was to be convicted, they could not rely on this. They would need other evidence directly linking him to the scene.