"THE BEST WAY OUT IS ALWAYS THROUGH"
Detective Marcus Bell of the 11th Precinct was dating Detective Shauna Scott of the 12th Precinct. What Bell didn't know was that Scott was also working for the Internal Affairs Bureau....
Since the series is about the Sherlock Holmes of the modern age in a world in which Arthur Conan Doyle never took credit for the stories about a similarly named consulting detective in the Victorian era, of which there is no mention in 'Elementary', I've placed the show in the same TV dimension as 'Sleepy Hollow'. For that series, Washington Irving apparently never wrote about Ichabod Crane who - like Sherlock - exists in the modern age (although he did begin life in the Colonial period.)
I bring up Detective Scott because of her job at the 12th Precinct. A few other cops from the 12th Precinct in the overall Toobworld Dynamic are Detectives Beckett, Esposito, and Ryan from the series 'Castle', Detective Reagan and Sgt. Renzulli of 'Blue Bloods', and of course, there's 'Barney Miller' and his squad in the original 12th Precinct building which is now a museum dedicated to Police Commissioner Theodore Roosevelt. It has also "guest starred" in two shows in the 'Law & Order' franchise: 'Criminal Intent' and 'Special Victims Unit'.
Of them all, 'Barney Miller' and the 'L&O' franchise are the only ones that takes place in Earth Prime-Time. (I wrote about the 12th Precinct back in 2009.)
However, all of those other characters from the 12th Precincts in those other TV dimensions could conceivably be found in the main Toobworld as well. Not that all of them would still be stationed at the 12th, nor would they all have to be on the same shift. And even if they were, there are several floors in the new precinct building so their paths would never have to cross with each other. Besides which, no current show located in the main Toobworld takes place at the 12th Precinct, so it's not like we're going to see them bump into each other anyway.