I also live in the area described and his description is accurate. It is indeed a holding facility meant to keep people in and has direct rail access. If you go around it you will be stopped and yes they have black unmarked helicopters. The site has been operational, guarded and yet unoccupied for years now. I was taken through the facility to make repairs on equipment and I am sure its a detention facility.
Why not, it is an Amtrak Repair Facility.
http://www.wishtv.com/dpp/news/local/marion_county/indiana-amtrak-workers-assured-jobs-secure
http://www.fox59.com/wxin-amtrack-indiana-facility-080609,0,6070714.story