Police are investigating whether an alleged link between the poisoning of Sergei Skripal and the death of a spy whose body was found in a bag.
When the body of Gareth Williams, who worked for GCHQ and MI6, was found eight years ago, his death was attributed to a sex game gone wrong.
But following the poisoning of Sergei and Yulia Skripal in Salisbury, the incident is thought to be back under the spotlight.
Boris Karpichkov, a former KGB spy who claims Williams, 31, was murdered, is set to be questioned by counter-terror detectives this week.
The 59-year-old told the Sunday People: Russian security services are the connection between the two cases.
Williams remains were found in a locked red holdall in the bath at his home in London and Karpichkov has extensively studied the case.
He believes untraceable poison was used to murder Williams after he discovered the identity of a Russian mole infiltrating GCHQ.
Initially, Russia hoped to recruit him as a double agent, according to Karpichkov, by threatening to reveal his interest in cross dressing.
Karpichkov said: Williams had no intention of letting the Russians blackmail him.
But he was foolish enough to say that he knew the person who tipped them off.
When the blackmail attempt failed, Williams was presented with a bottle of wine and believed it was handed to him to make amends, Karpichkov said.
But it was spiked and caused him to pass out, before a specialist Russian unit arrived, using poison to kill Williams.
At the time, an inquest found that his death was likely to have been criminally meditated.
But a police investigation ruled it an accident, stating that Williams likely died when a sex game went wrong.