Russian authorities have previously claimed the dissident's death was not suspicious but had been caused as a result of "combined diseases". But Yvette Cooper said the UK and its allies had been working "with fierce determination" to establish what really happened. An Ecuadorian dart frog's poison is 200 times stronger than morphine. SUBSCRIBE to our YouTube channel for more videos: http://www.youtube.com/skynews Follow us on Twitter: https://twitter.com/skynews Like us on Facebook: https://www.facebook.com/skynews Follow us on Instagram: https://www.instagram.com/skynews Follow us on TikTok: https://www.tiktok.com/@skynews For more content go to http://news.sky.com and download our apps: Apple https://itunes.apple.com/gb/app/sky-news/id316391924?mt=8 Android https://play.google.com/store/apps/details?id=com.bskyb.skynews.android&hl=en_GB Sky News Daily podcast is available for free here: https://podfollow.com/skynewsdaily/ To enquire about licensing Sky News content, you can find more information here: https://news.sky.com/info/library-sales