In chapter 56 of ACOK, several of Theon's men are murdered:
Outside his door, Reek waited with Urzen and Kromm. Theon fell in with them. These days, he took guards with him everywhere he went, even to the privy. Winterfell wanted him dead. The very night they had returned from Acorn Water, Gelmarr the Grim had tumbled down some steps and broken his back. The next day, Aggar turned up with his throat slit ear to ear. Gynir Rednose became so wary that he shunned wine, took to sleeping in byrnie, coif, and helm, and adopted the noisiest dog in the kennels to give him warning should anyone try to steal up on his sleeping place. All the same, one morning the castle woke to the sound of the little dog barking wildly. They found the pup racing around the well, and Rednose floating in it, drowned.”
Who killed these men?