Downie looked up at her. ‘Try asking around the neighbours – someone may have taken photos or videos of the fire. It’s amazing how often the offender stays on to watch the fun.’

‘It’s already been done. Right now, I just need you to concentrate on your own job.’

‘OK. So . . . Locate seat of fire. Consider possible ignition sources. Excavate seat?’ Downie tilted his head to one side and looked at the charred remains around him. ‘Yes, I think so. Then take samples, formulate hypotheses. And report conclusion.’

‘I’ll look forward to it,’ said Fry.

Downie was unpacking what looked like a series of pre-prepared forms. ‘You’ll get a location plan, as well as photographs as I excavate the seat of the fire. Samples will go straight to the lab.’

‘Fine.’

‘By the way, I examined the outside of the building before I came in. Do you know that you have unsooted broken glass in the vicinity of a side window?’

Fry had been about to leave the room, but turned back. ‘What?’

‘A broken side window. I wondered if your people had noticed it already. There don’t seem to be any markers round there.’

‘A lot of these windows are broken,’ said Fry. ‘That’s the result of heat from the fire, surely?’

Downie looked up and smiled. ‘If that were the case, the glass would be sooted on the interior surface. It isn’t, which implies it must have been broken either in the early stages of the fire – or before it started.’

‘You mean a point of entry?’

‘Could be. I took samples anyway. But you might want to get that window examined for fingerprints or tool marks before the evidence is compromised any further.’

‘You don’t have to tell me my job.’

Downie just sniffed, as if she wasn’t even worth a reply.

Fry glared at the back of his head as he continued to lay out his equipment. Looking around for someone to give instructions to, she caught sight of the fire officer standing in the doorway, grinning.

At that moment, her phone rang. It was the sergeant in charge of the search team.

‘I thought you’d want to know straightaway, we’ve found an empty lighter fluid can. It’s butane, but quite an unusual brand, I believe. It looks like someone found a use for a hundred millilitres of Swan Extra Refined recently.’

‘Where did you find it? How near the house?’

‘It had been chucked in a wheelie bin a hundred yards down the street, near the corner of Lilac Avenue. The householder says no one at this address smokes, and she has no idea how the can got in her bin. She insists it wasn’t there on Sunday when she last put some rubbish out.’

‘You’ve got it bagged properly?’

‘You bet.’

‘Thanks.’

Fry ended the call and turned back to Downie. ‘Show me this side window,’ she said.