The very act of torture requires a level of emotional depravity that merely killing does not.
The nature of torture aside, taking the life of a sentient being is the ultimate violation of its rights. I don't see how any act less than killing can be considered morally worse than killing.
This does not make it right for a human to deliberately cause harm to an animal for pleasure or entertainment. I also would consider trophy hunting to be immoral if one leaves the body to rot.
Why?