Inside, the CSIs had rigged up lights. Like the flat we’d been to previously, there was no electricity and no heating. Three plastic garden chairs were scattered about the room. Cardboard boxes were stacked flat against a graffiti-sprayed wall. A sleeping bag lay over the top of the boxes with a bin liner. On the opposite side of the room, a king-size mattress lay – filthy and stained – on a layer of grey breeze-blocks, butting up against the concrete render of the wall. Lying on his back, in the middle of the mattress, in a sticky mass of congealing blood, was ten-year-old Ali Kousa. In the centre of his forehead, a bullet wound was matted with blood and his child’s features were contorted into a hideous expression of agony.

I gasped. It was a truly awful way to die.

Dr Clark was taking fingerprints from the body. ‘That’s one entry wound. Straight through and out the other side.’

Under the bright artificial lights, the pool of blood beneath his head looked black.

‘Where’s the bullet?’

‘We’re not sure if it’s in the mattress or somewhere else in the room.’

To the left of Ali’s chest, another bullet had torn through his sweatshirt and ripped a hole in his heart. ‘Whoever fired these bullets knew exactly where to place them. This isn’t a murder. It’s an assassination.’ I looked away, biting back tears. ‘Any idea as to the type of firearm?’

‘Kevin says it’s likely to be a pistol.’

Around the room the CSIs were photographing the blood spatter and marking out the angles, trajectory and pattern with string. Another CSI was spraying luminol. On the wall, the words the killer had scrawled in blood, seemed a cruel irony.

STREET RAT

A dart of fierce anger jabbed at me. ‘Poor kid. He escapes from Syria and manages to get himself to the UK, and he ends up getting drawn into God knows what, living in a squat with a load of junkies and having his brains blasted out.’ I took in the room. The bucket in the corner. The empty dope bags on the floor. The used syringe on the ground by the mattress. ‘What the hell did he do to deserve this?’ I was struggling to keep my composure.

‘If it’s any consolation, at least he’ll have died quickly.’ Dr Clark’s face was pale. ‘He’ll have been unconscious almost immediately, and bled out in minutes.’

‘What Jackie said is right, Maya,’ Dan said. ‘This is organised crime. These kids are being groomed and exploited because they’re desperate.’

Their words washed over me as something caught my attention. On the mattress, one of Ali’s feet was bare where his shoe had come off. Had there been a struggle? Had he been overpowered? Then, on the concrete floor, I saw his trainer. It was a dirty white with broken laces.

And was so small.

‘Street rats.’