With Stussy now revealed neutral and probably not the mole, it only makes sense for him to be
He has Caesar and VPs DF research, VPs lineage factor research, Queens and Caesars chemicals (poisons).
As pointed out before, he has way more sway or did with the WG than other kingdoms. He was said to have been able to avoid the fate of the others. He's underworld despite being part of the WG till now and Queen is the ONLY one who admitted to knowing him. Caesar said nothing, VP pointed out nothing, and Queen wasn't just a rival he also called Judge a bastard.
He totally sold them out for brownie points with the WG.