so, i do find there is an address holding 24 btc and got transactions from some suspicious addresses.
can I report this address or red flag it so that the scammer can't transfer the money anymore?
No because bitcoin is not centralized to have any option that would prevent anybody from spending their own money. The only possible scenario is if a government pressured a centralized service (like a shop accepting bitcoin payments in that government's jurisdiction) to refuse receiving payment from a certain address. But that still can't prevent the owner from spending their coins or moving them to a different address then making the payment.
There is another possible scenario.
You can monitor those coins, and once they go to some centralized exchange like binance/coinbase you can inform the police and the exchange so the
exchange freeze the funds.
You cannot stop coins flowing through the blockchain, but when he tries to convert btc into fiat (through exchanges) it is possible to get them back.
How do you tell when or if the coins ever left the possession of the (alleged) criminal, though?
Imagine how unfair it would be if this person bought a laptop with these stolen (just as an example) Bitcoin. Then the laptop seller used those BTC to get haircuts for himself and his whole family, and now the barber wants to exchange the coins they received, for fiat, to pay bills. Now the exchange is supposed to freeze the barber's honestly earned coins, just because they could be traced back to a criminal?
I strongly disagree with this. Why punish an innocent person?
Do note that there is no way to tell whether the criminal just bounced coins between their own handful of wallets, or whether actual money transfers happened like in the scenario I described.
But to prevent innocent users' coins to be frozen or confiscated, we need to accept each and every coin, even if we suspect it could originate from a crime and still be in possession of that person. Because there's no way to tell for sure, except if they never moved it at all.