To those who knew him to any extent, he was seen as pretty normal. Above average at school, fond of football, a fan of Tottenham Hotspur and an amateur centre field player. Most of the accounts initially were reasonably positive. By the following day the story was a bit more nuanced. He had punched a girl in the face 10 years ago. He was aggressive. He was a big guy and you wouldn’t want to get on the wrong side of him. He had a very difficult father, who contributed nothing much to his upbringing. No-one had any inclination he would do a thing like that, though he had become a preacher, though not about Jesus.
With a confederate he rammed a car into an off duty soldier, cut his head off with a meat cleaver, dismembered his body with knives and machetes, and then for 20 minutes posed for photographs and gave interviews in which he gave his justifications and issued threats. Some extremely brave women passers-by (one getting off her passing bus for the express purpose of helping the fallen man) engaged the murderers in conversation. They reported that the main protagonist was apparently neither drunk nor on drugs, just an angry guy.
Murder is too rare a behaviour in for the average citizen to pick up warning signals. Too rare for the security services as well, who knew of lead protagonist, but not of his most recent Jihadist plans. With any luck a fuller picture will emerge, though probably never a way of distinguishing the noise of the average angry guy who converts to Islam and preaches anger from the signal that two butchers are hunting for an English soldier walking one afternoon on a English street.