[... Call me up, I will take you down there myself…so you can put the pieces of this puzzle together.]
Just for the record, Steve asked me to transcribe his letter verbatim. However, he writes like he talks -- jockularly -- and made a boast of 'taking you down there myself'. Obviously, he does not have the authority to do this, and has long since retired from the NYPD. Whenever he 'investigated' the tunnels, he was doing so either as an employee of NYCTA or the NYPD, or was otherwise in the company of an authorized employee of NYCT.
Subway tunnels are not for public access and it is illegal for non-NYCT employees to be found in them. With this in mind, let's relax, take a deep breath, and do 'paperwork' investigations into these mysteries -- a perfectly legal approach.