Evgenia Kara-Murza has no doubts who was responsible for the death of Russian opposition politician Alexei Navalny in prison on Friday.
"Make no mistake, this was a political assassination and murder carried out in cold blood, and the man responsible is Vladimir Putin," she told 7.30.
"The reason Alexei Navalny had to be eliminated like that is because he represented a very strong alternative to Vladimir Putin and refused to back down, refused to be silenced."
Ms Kara-Murza is the wife of opposition politician Vladimir Kara-Murza, a Putin critic who was jailed in 2022, after returning to Moscow.
Her 42-year-old husband is currently in solitary confinement in a prison colony in Siberia, where he is serving a 25-year sentence for speaking out against Mr Putin's war in Ukraine.
Like Mr Navalny, he survived poisoning attempts with the nerve agent Novichok. In Mr Kara-Murza's case it happened twice.
"My heart goes out to Alexei's family, and I can imagine what they're living through right now because I've been on the brink of that, at least twice," Ms Kara-Murza said.
"But this is still something too huge to process. And I believe that millions of Russians who have been absolutely horrified by Alexei's death have not yet been able to process it."
Ms Kara-Murza says if you look at the history of Russia under Putin, it's no real shock that Navalny did not survive his prison sentence.
"I was horrified, of course, but unfortunately not surprised, because political assassinations are something Vladimir Putin has been doing for years," she said.
"Novaya Gazeta, one independent media outlet alone, lost six employees to political assassinations over the years.
"In 2015, the leader of the Russian opposition, Boris Nemtsov, was assassinated 100 yards away from the Kremlin walls.
"Today it was Alexei Navalny after they tried to kill him with poison."
Russia denies Navalny was murderedRussian authorities deny Navalny was assassinated, saying he died of "sudden death syndrome" after going for a walk in the Arctic penal colony where he was serving over 30 years in prison.
However, his team believe he was murdered and say the fact that authorities have refused to release his body to his family suggests there is a cover-up.
Ms Kara-Murza says she doesn't believe the Kremlin's version of events.
"So far, the Russian authorities have offered two possible reasons for Alexei's death. And that's sudden death syndrome or blood clot," she said.
"I've heard those ridiculous things after my husband's poisonings, both poisonings in which he was given a 5 per cent chance of survival twice.
"So, I know what they say when they kill someone."
John Sweeney is a British journalist who has been covering both Mr Putin's wars and the deaths of his critics for over two decades.
His book Killer in the Kremlin documents what happened to those who dare to take on Mr Putin.
He told 7.30 there is a sordid history of his critics being rubbed out.
"Let's run through a few of them," he said.
"Anna Politkovskaya, Natasha Estemirova, Boris Nemtsov, Alexei Navalny.
"In that order. Poisoned then shot. Shot. Shot. Poisoned, now dead. I've met all four. All four were very critical of Putin. All four are dead."
Sweeney believes Navalny was murdered.
"The message from the Kremlin is, don't mess with the Tsar because if you mess with the Tsar, you may die," he said.
Sweeney says the 47-year-old posed the greatest threat to Mr Putin of any Russian politician.
First Navalny was barred from running for president, then he was poisoned in 2020. After recovering in Berlin, he returned to Moscow in 2021, where he was arrested at the airport and eventually jailed.
"He [Navalny] was everything Putin wasn't — physically brave, amusing, funny, charismatic, all of those things," Sweeney said.
"I think tyrants hate being mocked. He was on the blackest of blacklists, and he wasn't scared. He stood up to Putin and he stuck it to him.
Putin is 'scared to death'"Putin hated him. You look at the pictures on the day his death was announced, Putin looked so happy."
Human rights activist Bill Browder is another person with a deep knowledge of how President Putin operates.
Once Russia's largest foreign investor, he was banned from the country after he exposed corruption linked to the Kremlin.
He now heads up the Global Magnitsky Justice Campaign which aims to hold human rights abusers in Russia to account through sanctions.
He worked with Navalny to expose corruption in Russia and believes that his friend was murdered.
"Putin's got an election coming up in the middle of March. He's scared to death that people aren't going to come out and support him. He's scared to death of the opposition," Mr Browder told 7.30.
"What better way to make sure that he has no opposition than to kill the most important opposition politician in Russia, Alexei Navalny?"
He says his friend was a man of immense courage, who returned to his country at great risk to himself after recovering from his poisoning.
"At that moment, the Putin regime said if you come back to Russia, we will arrest you, hoping that he will never come back to Russia. But instead he got on that aeroplane, flew to Moscow and was arrested," he said.
"It showed what kind of man Alexei Navalny is. He cared more about the future of his country than his own personal security and his own safety, and he was ready to take a risk with his life and his liberty for his country."
Over the weekend over 400 Russians who had been commemorating Navalny's death across the country were arrested.
In the current climate, Ms Kara-Murza is worried that her husband and other political prisoners may not survive.
"Yes. I do believe that his life is in danger," she said of her husband of 20 years, and the father of her three children.
"As are the lives of many other Russian political prisoners held behind bars in Putin's prisons, and the lives of Ukrainian civilian hostages and war prisoners held in Russian prisons, as well as our colleagues who oppose Alexander Lukashenko in Belarus.
"I have been fearing for my husband's life every single day since at least his first poisoning in 2015.
"I have been sleeping with my phone by my pillow all these years, just knowing that any moment of any day of my life, the phone call might come."