What does "His alibi checks"mean

'Checking his alibis.' Which words confuse you? There are no idioms in the phrase you posted.

It's probably a response to the request "Check out his alibi." An alibi is a set of circumstances that eliminates you from being suspected as the perpetrator of a crime through witness availability or data that proves you were not at the scene of the crime. 'Checks out' means the circumstances you claimed happened really did and the investigation verified your words and actions as fact. Thanks

I don't know what "his alibi checks" mean. I don't know what else I can say.

Does this mean that he has an alibi?

Yes, he has one and it was verified. The evidence tells the same story as his words -they are in agreement -they check. So, the alibi isn't fictional -It checks. It's legit. Moreover, he can be checked off as a possible suspect from the list now. He's free of suspicion when his alibi checks. Thanks