Bill Browder, who has been described as Vladimir Putin's number one enemy, says the poisoning of Sergei Skripal in England was an act of terrorism by Russia.
Mr Browder was an American-born finance executive in Russia who was refused entry to the country in 2005 as a threat to national security.
He claimed it was because he and his lawyer Sergei Magnitsky had exposed corruption in the country.
Mr Magnitsky died while being held in prison in Russia. In a posthumous case against the lawyer, Mr Browder was indicted and tried in absentia. He was convicted and sentenced to nine years in prison.
Mr Browder told Morning Report Mr Skripal's poisoning fitted the Russian government's modus operandi, with strong similarities to the 2006 death of Alexander Litvinenko, a defector and former officer of the Russian FSB secret service who died from radiation poisoning in London.
Mr Skripal and his daughter are both in critical condition after a chemical attack on them in England. Mr Skripal had been a Russian spy before defecting to England and working with MI6.
"This is a man considered to be a traitor to security services in Russia; nerve agent can only be produced by a government; what else could it be but a Russian hit in the UK?" Mr Browder told Morning Report.
Mr Browder said the killing of Mr Litvinenko and lack of serious repercussions had created an environment where Mr Putin and the Russian government felt they could get away with these kinds of attacks.
"I don't think Putin really cared one way or another about this individual, but he cares very profoundly about all the other people around him who are less and less loyal to him because the money is drying up in Russia," he said.
"People are starting to privately grumble and Putin's way of dealing with that is to terrorise them.
"He's sent the most powerful message to everybody around him that if you even think about doing something which is disloyal, terrible things will not just happen to you, they will happen to your family."
Mr Browder said Russia wanted legal deniability but was winking and nudging about the attack.
"They got caught last time when they did the same type of thing with nuclear materials with Litvinenko. They were very happy because there were no consequences."
As an enemy of the Russian government, Mr Browder said he was at risk of a similar attack and had already faced death threats, kidnapping threats and extradition threats.
However, he says he was not living in fear.
"I continue to live with a clean, balanced psychology because if I lived in fear they would have already achieved their objective and I'm not going to let them do that."
Mr Browder said he could not describe the types of precautions he takes in his own life as it would provide the Russian government with too much information.