It was the most quintessential London scene: a Friday morning bathed in dappled sunlight in Putney, an upmarket yet unflashy corner of the city. The kind of place where bankers settle down with their young families for a change of pace. There were commuters making their way over Putney Bridge to work. A brown-haired man, running in a gray T-shirt and dark shorts. A red bus rolling along the road. Nothing you would expect to watch again on CCTV, or to go viral, garnering millions of views on social media, or result in a near decade-long investigation.

But that’s what happened on May 5, 2017, at 7:40 a.m., when, out of nowhere, the runner in the gray jersey suddenly shoved a female pedestrian walking the other way straight into the path of the oncoming double-decker bus. By some stroke of luck, or quick thinking, or fate, as the woman flew from the sidewalk and onto the road, the driver swerved in the nick of time and rushed to check on her. “What happened?” he recalls her asking, and “Why? Why? Why? Why me?” The entire country was wondering the same thing.