David controls the tourism industry in the local area he control where the Kine travel too from the shadows. He has a powerful ghoul on each of his controlled island and takes it over. Making sure they control or at least influence the tourism industry on a local level. David works through processies hiding behind an army of ghouls and servants. After the Hecata take over he will move quickly to stop the tourism almost completely to Syros this is not difficult due to the recent murders, explosions and such. So using that he is able to strip the supply of Kine. Basically starving them out. He will also tighten watch over who comes and goes to the island through his side, he does not take over the stuff on the Hecata side no instead reading between the lines so to speak. Its all about subtle influence.
 
Davids role is the leader of the conspiracy is not exactly true as he serves someone above him. He is basically untouchable since he controls where the kine move and for these islands this is the lifeblood. As such his influence is vast. 
 
Sebastian will look into David but for once actually come out a bit short. He does find basic info formation however tracking his influence will be difficult. Especially when the Kine start to not come here as David and his minions all are masters of controlling things from the shadows. 
 
His response to the dirt given to the Prince will be a tactical one, for one other Ventrue will challenge the Prince on this ruling as it is a Brujah prince. There are many disenfranchised Ventrue in the city who will work against the Princes small political power. They will band together creating many favours to gain allies. They will be less overt playing nice. If the Si papers comes out to the Prince the Ventrue and many who have fallen to there side will demand a lengthy investigation. The Prince can not move against him directly needing to do the honours for a thorough investigation lest he insults the clan.