If you have any evidence of this, then pass it to the regulator...

If you have any evidence of this, then pass it to the regulator as self dealing is a no-no, according to the rules. I'm not sure though how it exactly makes a directional impact though. If XXX and ZZZ are controlled by the same person, then if XXX buys or sells to ZZZ, then there is no change to anyone else. There may be a false impression of liquidity in the stock, but which direction does the stock price move? The usual story in these situations is a pump-and-dump idea, which is opposite to what you're talking about. Anyway, once they've done the trade, all anyone can see is a trade and the person controlling both accounts is in a net zero position so that what they make in one account, they lose on the other. The controller of XXX and ZZZ needs someone else to trade with them if they are going to make money out of this scheme and you haven't outlined how they come into it.