There is no doubt that Castle Alley had a dubious reputation - a surveyor for Charles Booth's Map of London Poverty in 1898 described it thus:"..under arch into Castle Alley. No houses, factories on either side, two of the Whitechapel Murders were committed at the south end. This street is quiet and used as a place of rest by the dwellers in the Whitechapel Lodging Houses. By custom, women sit on the west side of the pavement, men on the east."
(Actually, I don't know of any of the Ripper murders/body-dumps which occurred at this location.)
Lower on the same web-page, there's a photo of the site where McKenzie's body was found, captioned "Old Castle Street, looking north, 2005 (Robert Clack)." So, you might be able to understand my confusion. After trying to pin down the locations, I've noticed time and time again that all sorts of pointless details are provided, and yet the location is usually glossed over. In this case, they provided a misleading statement (which is actually the only time I saw a definite, precise location mentioned in print), along with a vaguely identified photo of the actual location - and this is supposedly one of the more authoritative sites.
In retrospect, Google Map's apparent plotting-error (shown at top) put the marker closer to the correct site, although the arrow indicated the precise location (of the erroneous coordinates). My previous revision of the pentagram-map also had it closer to the correct location, but I don't remember where I got the information.