2 things bothered me (spoilers)

and it is most likely not what you'd it expect to be. well, maybe i just did not take enough attention, so maybe you guys can help me out.

1. was there any real motivation for his girlfriend to "take over" the book? you know what i mean? apart from wanting that power, why would she try to pull the stunt she did.

2. the detective concluded, that kira must know the face and the name, which is accurate, BUT how did he deduct that? i mean it is one thing to come up with the idea from the view of the author, but how the hell would a character come to such conclusion. on it's own, it is a rather outlandish idea. i mean, imagine you'd be a cop. how many theories would you go through, before you land at: "it is done remotely, through some supernatural force, the attacker needs to know the face and full name of the victim and even though over 500 people have been killed, the teenage son of the police chief must be it". not to speak of the press conference, where he got his turtleneck over his face. there wasn't a more believable way to cover/distort his face?