Why?

Why does there have to be such evil people in this world?  I don't understand how some human beings can do the things that they do.  Maybe they aren't really human - they have no soul - they have no heart.  What I am referring to is that someone killed a mother turtle with a knife last night on the beach and didn't even take her away for eating purposes - just killed her for the sake of it.  Why? Why would someone do such a horrible thing?

Gary and I were walking on the beach this morning and walked up on two people with the turtle preservation group - and they were taking pictures and cleaning up the beach location.  We stopped and talked with them and they told us that a mother turtle had come up on the beach and laid her eggs and then was headed back to sea - and someone stabbed her with a knife and then just left her there to die.  The killers did, of course, rob the nest of all the fresh turtle eggs.
I understand that turtle eggs are good to eat and a delicacy, but seriously - why did they have to kill the mother and just leave her there to die?