If anyone has 2hrs spare (because that's how long it took me to read this exhaustive investigation piece by BuzzFeed News) then this long read on assassinations taking place in London of enemies of Vladimir Putin that have been easily ignored by British authorities.
The murder of Alexander Litvinenko was the prominent killing in 2006 that led to diplomatic relations between the two countries dissipating and a public inquiry concluding it was probably authorised by the main man himself, Putin, but no idea how long the list of murders linked to Russian secret authorities there were.
It shows the depth of intelligence they have in Russia that they can kill someone and frame it so that the authorities are easily inclined to say it was suicide; intimidate to the point people kill themselves.