Who kills Cosmo?

Could you please provide some further context or details regarding the paragraph "Who kills Cosmo?"? It seems to be a rather intriguing question, but without more information, it's difficult to offer a comprehensive description. Are there any specific characters, events, or plotlines involved? Is this from a book, movie, TV show, or real-life incident? Also, are there any clues or hints that might suggest who the killer is? With these details, I can better simulate the tone of a questioner and craft a description that satisfies your requirements.