In case you were wondering what the Impala's been up to during all of this, we get a shot of the car still cooling its jets in front of the building. Hey, you snag a sweet parking spot like that in the middle of a major city? You're likely not moving the thing for months.
Sam and Jo futz around with pieces of photographic research at the kitchen table as Dean enters to identify the latest victim as "Theresa Ellis." Dean also fills the other two in on the cracks in the plaster and the spooge stains dripping all over the place, and everyone looks glum. That is, until Jo draws a previously ignored photograph from the pile to announce, "Maybe we're looking in the wrong place." It's an old picture of the field that occupied the current building's lot. Next door? A jail. DOY! Like they wouldn't have noticed that sooner. WHATEVER, Supernatural!
Jo gets off the phone with Ash to inform the boys that the rehabbed warehouse in which they stand was once next door to Philadelphia's infamous Moyamensing Prison, "built in 1835, torn down in 1963," and no, it opened in 1835, closed in 1963, and was eventually torn down in 1968, but that's a minor quibble compared to some of the ones coming up, so let's drop it and get to the real point of this conversation -- the field next door to the prison complex was used for executions before the state assumed control of capital cases in 1913. Soon enough, the boys are scrolling through an Ash-provided list of every person hanged in the field next to Moyamensing. Alas, there are one hundred fifty-seven names on that list, so I suppose it's a really good thing College Boy almost immediately gloms on to the one that's relevant: Herman Webster Mudgett, better known as H. H. Holmes, better known still as The Beast Of Chicago, who admitted to torturing and murdering at least twenty-seven people in the years surrounding the World Columbian Exposition of 1893. One of his weapons of choice, which the show gets correct, was chloroform, which is what Dean smelled in the hallway the previous evening. What the show gets very badly incorrect, however, is Holmes's "victim of choice," which Dean claims to be pretty young blondes, but which actually was pretty much anyone the guy could get his hands on, so again: WHATEVER, Supernatural! In any event, while they'd love to salt and burn his bones and thus be done with him for good, Holmes directed his body be "encased in a couple of tons of concrete," as Sam more-or-less correctly puts it, so Our Intrepid Heroes (Plus Heroine!) are shit out of luck. Just then, Sam realizes something even more depressing: Holmes's Castle in Chicago, the hotel-slash-human charnel house he built to lure guests during the World's Fair, was replete with trap doors and secret rooms and such, so that means his evil spirit must be using similarly hidden crawl spaces in the present building to store his latest victims. Okay. We'll go with that. For now.