It doesn’t seem like the police did much about it because in GGO you have XaXa on the loose, the police probably couldn’t have done much, but they should’ve tried and caught at least a few members.
IIRC everyone - including Kirito - got official pardons for actions taken within the game. Even if they’d brought members of Laughing Coffin to trial, the fact that “it’s just a game” gives them plausible deniability. A conviction would have been extremely difficult.
It’s largely established that the government has effectively no visibility into anything that happened within SAO, and all SAO players were given pardons for actions that happened in the game in part to save face but also in part because “it’s just a game” might be actually become a valid legal defense, plus there’s no evidence to base decisions on.
All SAO players who were of school age were sent to a special remedial school to try to get them back up to speed, which included regular psychological evaluations, which theoretically should help many of the laughing coffin members learn to handle things in a more healthy manner, but obviously it’s established that some are just criminally insane. I don’t think they ever really cleared up what happened to adult SAO players upon being released so that’s an obvious opportunity for more laughing coffin players to pose a threat in future media
