It is a small bit of trickery masquerading as generosity: A suspect is offered a cigarette or a soft drink in a police interrogation room.

The ruse is a staple of television crime dramas. Detective so-and-so asks questions; the suspect does not cooperate, but unwittingly leaves damning DNA on a cigarette butt or a soda can. Cue the handcuffs. Roll the credits.

But in the detective squad rooms of New York City, the procedure is far from that simple.

Consider Section 4(a), which tells interrogators that when “providing a partially consumable object that is prepackaged by the manufacturer with other objects in a ‘pack’ type container (e.g. cigarettes, chewing gum), provide an unopened ‘pack’ type container to the suspect.”

Or Section 2(b), which calls for cleaning surfaces in reach of the suspect with a “solution consisting of a 10-to-1 ratio of water to bleach” and then drying those surfaces.