Saw 4 Plot holes. !WARNING! !SPOILER! DO NOT READ THIS IF YOU HAVE NOT SEEN THE MOVIE?

Ok few questions... Why did the detective become jigsaw's new apprentice? (are we suppose to know this already or do we just wait for saw 5?)... Next question: If the detective is already carrying out Jigsaw's work, why would jigsaw leave him a tape saying "my work will continue even though i'm dead"? (surely the detective already knows this)... And finally: Did the lawyer (the guy watching over mathews on the ice block and the detective in the chair) know the detective was the baddy???(if he DID know, then why go along with it? why not just kill the bad guy and help mathews and rigg.. If he DIDN'T know and the detective just let himself get abducted and strapped to the electric chair, how did he just get up out of the chair at the end with ease.