which killed 24 people, and he may have made a pilgrimage to the site.

There was also another promising lead. A man from Northern Ireland, Sean Toner, contacted police. His father, Hugh, had gone missing from a Craigavon hospital in 1994 and not been seen since. In photos, he bore a resemblance to the man in the CCTV images. But when a DNA sample was taken from Toner, it proved not to be a match.

But there was one theory that DS John Coleman kept returning to: that the mystery man had links to Pakistan. Police had discovered that Lytton had a 10cm metal plate inserted into his left leg between 2001 and 2015, which indicated that the operation had taken place in Pakistan. A container of medicine found onhis body was also linked to the country.

On the first anniversary of his death, police had a major breakthrough.

Speaking to the Guardian, Coleman said: “We started to concentrate on the Ealing area and looked at the train lines and where they travelled to.

“We already knew that this man had an operation in Pakistan in the last 10 years and we started looking into the theory that he could possibly have travelled alone from Pakistan to London Heathrow in the days leading up to his death.”

This began a process of trawling through hundreds of names of people who had boarded flights in the days leading up to 12 December 2015.

“The check of the flight names threw up a particular name. We then managed to get a passport for that