I also will give him a warning in the tone he uses to address others. As a moderator who can delete posts and not ban people he needs to be respecting our quest for a civil forum.
A warning seems insufficient. He has been very consistent in calling people names and making small personal attacks like this. But it's your site...
You should at least implement a policy that anybody with moderating ability should only post under their main name. It only seems fair for us to know if we are discussing with somebody who is capable of deleting any dissenting opinion. This would add weight to your pledge to "monitor" what Malmo deletes.