Sullivan

* See also Security Systems
* See also Laws_in_Rapture
* See also Criminals_In_Rapture
* See also Neptunes Bounty ( Investigation office in Wharf Master's Office )
* See also Culpepper ( as in 'alleged killing of' ... )
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Ryan's Security Man in Rapture 
The Novel had Sullivan working for Ryan on The Surface BEFORE Rapture even existed ( an ex-cop ).
He handled various investigations ( like the Fontaine's Smuggling Ring ) which threatened Rapture's Security and Existence.
We never actually saw what he looked like in-game ( except the little Audio Diary tile ) as he was already dead ...
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Culpepper Death with Sullivan the Alleged Perp :
Add Link to Culpepper Killing Audio Diary set
The given story has Sullivan doing the killing because Sander Cohen asked Ryan to have it done. Sullivan's Audio_Diaries about the Culpepper Killing supposedly makes up the Vague story 'evidence'. Sullivan doing it is inconsistent with his character. This is not an act of 'Carrying out The Law' as all his other actions have him doing.
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Consider : "Sander Cohen Is a Two Parts Suck-up and Ten Parts Hack. And That's Being Charitable." - Anna Culpepper :
Was this situation really Anna Culpepper's professional jealousy about Cohen being more famous, being more popular as a performer, having more influence, and making far more money than she did ???   SHE is in Rapture too, likely escaped from her own mediocrity on The Surface ( Why would Successful Artists come to Rapture ).   "Takes a Hack to know a Hack" ? 
It is totally possible that : She was really killed because she started to 'trash talk' Sander Cohen too much -- AND Quite Possibly it would be Cohen himself who would want to 'Do the Deed' ( Something logical with us seeing Cohen's later actions manifested towards 'Critics' ).
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At least it would have been little more likely/logical that she was killed because she started singing in support of the anarchist Atlas.  BUT, merely singing against Ryan's/Rapture's Philosophy is weak and inconsistent for Ryan -- As Grace Holloway was never even 'locked up' ... and Sofia Lamb merely 'got Exile' to Persephone for her Sedition, and NOT assassinated/killed ( which would have been easier/more-expedient ).  
Read it all again. There ARE other possibilities.  Those Audio Diaries might imply it, but there is no definite declaration/confirmation there.  
Treat it like one of those Mystery Stories where the real story isn't what it seems from first sight.  Sullivan saying "When it was done" -   could be just Sullivan confirming Culpepper's reported Suicide ... For some reason it is NOT 'spelled out' ( a 'smoking gun' in the game ) that HE 'did it'. ( Again : the vagueness of so many of the games Audio Diaries ... )
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Sullivan would need Detectives and Investigators for his Security Operations. A big part of Rapture's 'being secure' entailed looking for unauthorized connections to The Surface. Constables could be called in for enforcement once a crime had been found being committed.
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 From http://tvtropes.org/pmwiki/pmwiki.php/WMG/Bioshock   :
( Which is chock full of various speculations from before the Sequels Came out... )
Players Proposed Theory : Security Chief Sullivan Killed Suchong :
""Sullivan was one of the few people in Ryan's administration who seemed to notice how screwed up things were, and BioShock 2's loading quotes reveal he was the one who discovered Dr Suchong's body.  Feeling guilty over his own actions, and wanting to prevent more damage from being done by the mad scientist, he murdered Suchong and faked an audio tape to implicate a Big Daddy.  Furthermore, when we discover Suchong's body the drill seems stuck there, which would seem improbable if the hulking Big Daddy did it.""
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Quite possible if the Infinite BS DLC was all a hallucination which Elizabeth had as she was being Lobotomized/Shock-treated ( Remember her 'Trip to Paris' ... And all that Booker talking in her head stuff ... )
Why not have Elizabeth actually kill Suchong to hide her involvement in aiding Atlas ??? 
Once Alternate Universes are added into a story context, all kinds of things become possible.
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The Novel has Fontaine's thugs try to assassinate Sullivan as he investigates the Smuggling Operation. That is an indicator of the 'Hard Ball' being played in that situation, and [suspects up to get information] existed in the times 70 years ago On The Surface. 
Deliberate process Sullivan used. Gangsters don't do things this way.
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