The U.K. government’s response to the botched poisoning of a defected Russian spy was too weak and will embolden President Putin to carry out further attacks, according to one of the Kremlin’s most influential critics.

Financier and activist Bill Browder spoke to VICE News one year on from the nerve agent attack in Salisbury, England, which killed a member of the public and hospitalized former double agent Sergei Skripal and his daughter Yulia.

The British government has identified two Russian agents it believes carried out the attack and expelled Russian diplomats. But Browder believes they should have imposed further sanctions as a deterrent.

“The only consequence to Russia using military grade chemicals in Salisbury to assassinate their enemies is 23 diplomats being expelled,” he said. “Effectively, Vladimir Putin has been given a message by the British government — that he can get away with murder.”

Mr. Browder is himself considered a prominent Kremlin target. The hedge-fund-manager, once one of Russia’s biggest foreign investors, was kicked out of the country in 2005.

He lobbied the Magnitsky Act through Congress in the name of his lawyer, Sergei Magnitsky, who died in jail after uncovering massive tax fraud implicating Russian officials. It sanctions individuals linked with human rights abuses.

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