Emmerson Wain Manning, Practical Instruction for Detectives…
“ We will suppose that it is desired to keep under surveillance an employee of a bank, office or store. It is advisable in such cases that the person to be shadowed shall at no time see the detective if it can be so arranged. In my experience I have found that under most conditions the following plan will be most feasible for taking up surveillance of such persons. The plan applies also to any other occupants of such places. A detective other than the one who is to do the shadowing should visit the place where the person to be shadowed is located. ”
