Who verifies correctness/validity of evidence of violation transaction?

“If a validator violates either slashing condition, the evidence of the violation can be included into the blockchain as a transaction, at which point the validator’s entire deposit is taken away with a small “finder’s fee” given to the submitter of the evidence transaction. In current Ethereum, stopping the enforcement of a slashing condition
requires a successful 51% attack on Ethereum’s proof-of-work block proposer.”

Who verifies the correctness or validity of evidence of violating slashing conditions transaction and after how long? How long shall it take to slash violator’s deposit?