I found these videos that do an excellent job of showing where all of the detective case items are. I didn't make these videos, therefore I take no credit for them.
Cell block cases:
http://m.youtube.com/watch?v=GbMx2ATiwH8Administration cases:
http://m.youtube.com/watch?v=6_ulZ3A64eoIndustrial cases:
http://m.youtube.com/watch?v=pguFhlaeMOQ