The man had only been in the Philadelphia diner for about 20 minutes when something shot through the window and knocked his baseball cap clean off.

He was a regular at the Four Seasons on Cottman Avenue, though staff don’t recall his name, and had sat down with his wife to enjoy a sandwich at around 6pm.

It later turned out that the projectile was a small piece of metal that had been fired with the force of a bullet from a medical jet that plunged into a busy intersection some 350 yards away.

In seconds, northeast Philadelphia – one of the most densely-populated areas in one of the US’s biggest cities – went from having a normal Friday evening to witnessing scenes of death and mayhem.