Earlier quoted context omitted.
There is no actor in charge of surveilling the network. Every validator is. And every validator is incentivized to do so because you get a reward coming from the slash penalty. So everyone is checking on everyone else.
Validators only add transactions to the ledger. What I was talking about is the slasher, which makes sure nodes are behaving correctly.
Further reading: https://eth2book.info/altair/part2/incentives/slashing#the-v...
There is no separate notion of a slasher, everyone gets to provide slashing evidence when they build a block. I don't understand why you build such a weak straw-man and the push it forward as if it was the truth without even checking how the system operates.