In this Ted Talk Jim talks about how if you are born with a special chromosome and you experience a severe trauma then you could become a insane killer. In the Serial story Adnan was accused of killing his girlfriend after she broke up with him. This makes me think did he have that special gene to make him into a killer. I think that that is a very good possibility because he was dating this girl and then they broke up, that could be the trauma that caused the gene to be released causing him to kill his girlfriend. I don't know if this is what caused him to kill his girlfriend, i'm not even sure that he actually killed her. If he did kill her then this a a possible explanation as to why Adnan went from a nice cool teenager to a mean cold guy who would kill someone that he still loved.