Berezovsky emigrated to the UK in 2000 after falling out with President Vladimir Putin.
In fear of his life, he sought political asylum and moved to the South East of England, buying upmarket properties in Knightsbridge and Berkshire.
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Police believe it is a "distinct possibility" that Halliwell was a serial killer, beyond the two murders he was convicted for.
Tuesday's weather for the west of the region
Tuesday's weather for the east of the region