When I was growing up, my first experience with death was the death of Heidi, my guinea pig.  She was killed by my lop-eared rabbit, Brownie.  Of course, this wasn't a planned "hit" or anything.  When we were home, we let them wander around the house and they always got along.  They even ignored each other.  What I gathered from my mother was she had startled Brownie and the rabbit jumped up on top of Heidi's cage.