If they attack/kill a human in the ocean, who's gonna document them?
The other humans at the scene maybe? A single human alone in the ocean is not as common as you seem to think.
Orca's hunt in packs, and coordinate their attacks. So they might communicate to organize an attack on a group of humans. Here is a video of a pod of orcas executing a very organized training session to teach the juveniles orcas how to isolate and kill a crabeater seal on the pack ice. It is hard for me to believe that they could do this without some sort of high level communication. They are very intelligent animals.