This was my very first 55-fiction, about seven years ago.
He stood behind her in the elevator, a good four inches shorter. His hands accidentally brushed her bag, dropping it.
“Oops,” he said
“It’s ok,” she said, smiling.
He smiled back, and swiftly wound the metal string round her neck, tightening the noose until she slumped on the floor, still smiling at him.