I think Knut simply treats the carp as toys rather than wanting to murder them. Unfortunately the carps died when Knut fished them out to play with them.

Knut is leading a lonely life. This may explain why Knut likes the company with his keeper, Mr Thomas Doerflein, and his audience. I don't think Knut is a psycho or publicity-addicted. His fixation on humans may disappear when Knut has a female polar bear partner.