Bloody hell. I'd be devastated if someone had done that to mine. Mine really struggled for 2 days and I made the decision, I knew he was on borrowed time but no-one but the owner has the right to make the call.
Over the years I have seen a couple of times when a horse has been in physical distress, and mental distress of the owner has been seen as more important, and it has delayed the inevitable, to the detriment of the horse. I hope the horse in question does not get to the point where it is suffering, or likely to suffer, but if I thought it was, and it was on my property, I would have to end it.