Mrs Wilson invited us to sit down on the settee. We did, to make her comfortable. She sat down too, crossed her ankles and uncrossed them again.

Erica perched on the edge of the settee, opened her notebook and said, "In your own time, Mrs Wilson. Would you mind running through what happened once again?"

Mrs Wilson looked at her feet. "I went to pick up Bruce from school." She raised her head. Her gaze moved from Erica to me, back to Erica. Then back to the floor. "He wasn't there."

"You usually pick him up where, exactly?" I asked.

"No," Mrs Wilson said, shaking her head.

"No?"

She kept shaking her head. "Not 'usually'," she said, her voice louder. " Always. I always pick him up outside the school gates. I'm always there when the bell rings."

"And he wasn't there today?"

"That's right."

"He wasn't in his classroom?"

Mrs Wilson breathed in slowly. Didn't answer the question.

"Maybe one of the other parents…?"

Mrs Wilson was shaking her head furiously again, so Erica stopped talking, scribbled in her notebook.

I wondered if I should say something. After all, it was my case.

I was about to speak when Erica asked Mrs Wilson, "How can you be so sure?"

"I stay out of their business. They stay out of mine."

"What do you mean by that?" I asked.

Erica pursed her lips, probably annoyed with me for cutting her off.

"Nobody wants to hear about tragedy," Mrs Wilson said. "People want to get on with their lives and tragedy holds you up. Even someone else's tragedy can hold you up. It can infect you like some kind of wasting disease." She laughed without any trace of humour. "Surprised no one's asked me to wear a bell round my neck so they can hear me coming."