On 5 of the 6 sites where he has Electorate (all but SO) he stopped upvoting soon after 600 question upvotes. The most he has on any of those is 613.
Also, all of the badges are recent, suggesting that this trend started fairly recently (which is consistent with what we observed, namely that it started for us on Saturday)
Anyway, I think the evidence is rather strong. The supermods should be able to find more info quickly, like how many of his votes were cancelled recently on other sites. But the evidence that he's gaming the electorate badge network-wide and that he's serially upvoting here seem pretty strong in my opinion.