(((I think that's what he's suggesting. One of the criminals is using the book for evil purposes, and then Edward kills him. The partner then uses the page to kill john, and Edward, Edie, and the criminal have a big confrontation, and finally they knock the page out of his hand, and kill him with the book.
But, I like John threatening the police better. It seems to fit in more with Edward than the second option, because I think Edward would be discouraged after a criminal killing john to use the book, rather than it would be if Edward killed john himself. Edward is very twisted like that

))))
John almost screamed into the phone at Edward. "Yuzuki's about to jump out of her window because she found out about the Book! And it's all your fault!!" John roared.
"There's nothing we can do--" Edward began. "Yes, we can! You have to come her and talk to her! Get her to calm down!!" John said. Edward stopped running.
"....I don't think it's much of a good thing if either Edie or I show up....I think it's best if you handle it...." Edward said.
John muttered something, before folding the phone closed. However, the phone automatically went on speaker.
"Yuzuki!! Please, listen to me! Edward and Edie aren't doing this because they're evil people!!" John said. He paused, but it appeared he was getting no where.
"Yuzuki! Please, they're doing this for the good of the world!! Just listen.....If you want, I'll tell the police about them!! I just want you to be safe! And, maybe in prison, Edward and Edie could keep writing names!! Everything's going to be fine!!" John said.
Edward's eyes widened at this turn of events. John was willing to rat Edward and Edie out, only for Yuzuki? How would that help his plan, if he was in jail? Sure, he could write names with blood, but he'd have to smuggle the paper in somehow....No, too risky.
John would have to be done away with.