http://www.telegraph.co.uk/news/ukne...mss-death.html
The head of MI6 met Britain’s most senior policeman hours after the discovery of the body of a spy inside a locked holdall.
As for what Williams was working on and thus who might have wanted to kill him, this might be illuminating:
Mr Williams had been working at NSA shortly before his death, where he was helping to develop a joint GCHQ-NSA defence against cyber attack’s on the west’s computer infrastructure, particularly in the banking and transport sector.

At one stage during his work at NSA, shortly before he returned to London, Mr Williams was given security clearance to visit its facility in the Utah desert, which the agency classifies as “above top secret”.

Mr Williams also spent several months at Menwith Hill, the secret listening station in Yorkshire used by the United States to intercept coded messages, and Fort Meade in Maryland, the home of the NSA.