@cromat yeah we don't get the full story here but it honestly doesn't matter whether the threatening note come from Kurosaki himself or from the mafia because both scenarios do make sense in this arc. It can be from Kurosaki himself because forging that note himself is a much faster method to finish Hayashi off or it can come from the chinese mafia because they are told to cooperate or move on their own based on informations from Old Man Katsuragi or Hayase
If the note does come from the chinese mafia it also doesn't make sense to kill Hayashi on the spot because killing him won't enable them to get their own money back and at the same time they will get a lot of liabilities from doing crimes in public. It's much safer for them to threaten Hayashi slowly or let him surrender himself into the prison, if the stolen money is confiscated by the police then (at least afaik) that stolen money will be returned according to its irrespective owners (in this case, the 'clean' company owned by the chinese mafia) according the Organized Crime Penalties Article 13 (also mentioned several times in this arc)
That's my take on it anyway