When A Five Year Old Kill!

A five-year-old girl dragged a toddler to a bathtub and drowned him because he made too much noise and cried too much, according to police. This is  very troubling,upsetting,concerning,distressful, disturbing heavy   article. I got nothing but questions today.

Is a  5 year old capable of realizing that they can cause death to another human being?  Can a 5 year old grasp,get the picture comprehend at such a young age- that the act of holding a young baby’s head under water will lead to its death?