So it's the Mayor right?

The thing about Rhonda Perlman from the Wire being the accomplice is that she was pushing pretty hard initially to go after the family. Is that something she would have done if she was in on it? Also, Garrett says "he tried to kill me", which I assume was referencing the accomplice (although maybe not).

You're right that it could be someone else but there's two things which lead me to think the mayor. First is that it seemed real weird that this reporter would just be kidnapped more or less randomly by this guy. But it's less weird if you think that the mayor or the cop was involved and caught her snooping on them.

The second thing is that in these whodunits the killer is almost never just some random dude who is introduced in the finale. So who is it? There's not that many suspects left. Garrett was in jail, so it's not him. The older sister was sending the reporter after people so she would seem to have no motive to kill her. Tess seems like she would have been too young (although they lampshaded this a bit in an earlier episode). It could be the junkie brother. If it's not the cop or the mayor I think the most serious suspect is the mom. But we've known since the first ep that she was dirty so it won't be much of a shocking reveal if it turns out to be her.

Of course, the accomplice thing could be a red herring. We know that mom will go to extreme lengths to keep the secret. She might have murdered the reporter to provide a sort of alibi for her son.

Unless Alpert's covered in bacon grease, I don't think Hugo can track anything.