Police with expertise in environments contaminated with chemical, biological and nuclear material are searching the house of the late exiled Russian tycoon Boris Berezovsky.
Mr Berezovsky, 67, was found dead on Saturday, and a Thames Valley police cordon remains in place as police investigate his unexplained death.
The body remains at the Berkshire house while the search - described as a precaution - takes place, police said.
They say the public is not at risk.
The ambulance service was called to the Ascot house of Mr Berezovsky at 15:18 GMT on Saturday.
Wanted man
A Thames Valley police update said: "Specially trained officers are currently at the scene, including CBRN [chemical, biological, radiological, and nuclear] trained officers, who are conducting a number of searches as a precaution.
"This is to enable officers to carry out an investigation into the man's death."
[ embedded video inside ] - Boris Berezovsky led a colourful and controversial life
Supt Stuart Greenfield said: "We are aware the cordon is causing disruption to local residents and we apologise for any inconvenience, but it is important we take all necessary measures to ensure a full and thorough investigation can be carried out.
"I would like to reassure residents that we are confident there is no risk to the wider community."
He said the property was part of a large estate, so a number of roads were closed "and will remain so for the time being".
Mr Berezovsky was a wanted man in Russia, and an opponent of President Vladimir Putin.
A former Kremlin power-broker whose fortunes declined under Mr Putin, Mr Berezovsky emigrated to the UK in 2000.
Last year, Mr Berezovsky lost a £3bn ($4.7bn) damages claim against Chelsea Football Club owner Roman Abramovich.
BBC world affairs reporter Richard Galpin said sources have told him that Mr Berezovsky was depressed after the loss of the court case and was under financial pressure.
The tycoon's wealth is thought to have considerably diminished in recent years, leaving him struggling to pay debts in the wake of costly court cases.
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