To be rational for a moment, there are far worse ways of death than drowning both for animals and humans, and all the fish we eat drowned - in reverse, by oxgen intake, & we always seem to be unfazed by that.
We differentiate between pets/companions which we want treated well, and food animals that regretfully are destined to be prey, but that's the way life works.
Khandro, perhaps posting something like that on a news channel will make someone come forward with information that could lead to finding the scum who did this.