To say I am surprised that Russia is in the no 2 spot. And Japan is so high.

Precisely this.

It's almost a certainty that vast countries like China, India, Brazil and so on, with limited development and resources and huge, isolated, low-density populated areas are harbouring significant numbers of prolific, but entirely unrecognised serial killers.

Then there are the partially lawless States in Central and South America where violent crime and violent death are so commonplace that it will be entirely viable to be a prolific serial killer and not even make any attempt to hide your activity, but because the consequences are so indistinguishable from every-day events, law-enforcement will not recognise the results as serial-killings, or if they do, will probably attribute them to some other motive, gang-related, drug trade etc, than typical killing for the sake of killing. See Ciudad Juárez.

We have comparatively few serial-killers in Western countries now entirely because advances in policing and detection mean it's astonishingly rare to get beyond your 2nd or 3rd victim without being apprehended. It's much more difficult to actually meet the criterion to become a serial killer. Exceptions still occur, obviously, but it's changed days from the era of hand-written card databases and regional police forces who did not communicate.

This is just showing the ones they caught. Not the ones who are really clever and cover their tracks.

What Russia? They apparently didn't have any murders for a number of years as part of the propaganda about how great communism was. They didnt recognise the phenomenon if serial killers for years.
Instead they were / are murdering their citizens for Twitter posts.

These are the countries where police take their jobs seriously and aren't arresting autistic teenagers for homophobia against police officers or police horses, or checking people's Twitter for if they gave a scientific definition of woman.

The number of psychos and nonces is stable everywhere across the world in all populations.

The UK doesn't have a fucking clue how many people are here, doesn't value human life anyway, doesn't have a fit for purpose police force and you would never ever know or detect murder sprees most of the time.

Remember - this is going by IDENTIFIED serial killers. Countries with more developed policing systems, CCTv and judicial systems will always be higher because they catch more.

Why did you expect UK to be number 2?

Agree. Plus the government has a lot more control over the media in Russia than it does in some other countries. It would be much easier for them to keep it hushed up.

Oh god the real number for Russia is probably much higher - have you seen the size of that place? Sure there are entire communities decimated and vanished out in the wilds there by organised means, that no one else knows about. It would be even easier for one person acting alone to never be tracked.