It's hard to imagine which high karma person on LW would engage in individual persecution like that.
One can get sufficiently high karma rather easily. We are not necessarily speaking about the "top contributor" level here.
For example, if someone gets 10 karma points in a month, which is easy if they write regularly, they have 120 karma points in a year. If they don't downvote regularly, and only decide to drop the whole bomb on one person, that's 4×120 = 480 downvotes. Even if they spend half of it on regular downvoting, and the other half on a bomb, that's still "hundreds" of downvotes.
Below is a message I just got from jackk. Some specifics have been redacted 1) so that we can discuss general policy rather than the details of this specific case 2) because presumption of innocence, just in case there happens to be an innocuous explanation to this.
So... thoughts? I have mod powers, but when I was granted them I was basically just told to use them to fight spam; there was never any discussion of any other policy, and I don't feel like I have the authority to decide on the suitable course of action without consulting the rest of the community.