Russian spy poisoning: Why was Sergei Skripal attacked?

Almost eight months after the poisoning in Salisbury of the former Russian spy Sergei Skripal, the BBC has pieced together the extent to which he had been briefing foreign intelligence agencies before the attempt on his life.

Far from living quietly in retirement, Skripal had been travelling extensively across Europe and to the United States providing information to Western security services about Russian intelligence, including its alleged links with the mafia.

Richard Galpin has been investigating.