I'm sure this pops up a few times over the course of the series, but referring specifically to Season 6, why does Dexter choose to exclude Miami Metro from his findings that would easily lead to the capture of the Doomsday Killer (DDK). This in turn would save the lives of more innocent people. This to me doesn't seem to fit the 'code' Dexter follows.
I find it hard for him to justify certain kills that end up endangering numerous people that could so easily be saved. In earlier seasons, and even in this one, there are instances where Miami Metro have closed cases and he has found other evidence to link a person to a murder. This becomes an understandable path for him to follow, seek to get his own justice. I also understand the bigger cases that each season needs to follow still need to have Dexter exploring his own suspicions, but surely they need to give a better reason for him to withhold evidence from Miami Metro. If he has been seen by the person(s) in question, then obviously it becomes hard for him to share what he knows with his department, but specifically in Season 6, an opportunity arises where he can give away DDK's location without the need for further loss of innocent lives. This just seems to make a mockery of the 'code' he follows. Surely he can't be satisfied that his 'need' to kill is at the expense of innocent people being killed.