Looks like a lot of people here are new, thus they have rep of 25. If you want your accusation to really stick, you need to prove by showing that he sent some money to one or more of those accounts with rep 25.

You see, he would need all of those accounts to be funded with large amounts of steem power. Without that those votes are really worth nothing. If you can show that, then you have a valid point. Otherwise, it's just defamation.