Sometimes in an investigative scenario, the best clue you can acquire in a scene is the certainty that there is no information to be had.
For players, the “no-info” clue can help close off avenues of speculation, narrowing the focus of the investigation onto more fruitful paths. In the middle of an investigation, you may just have too many leads. A properly constructed GUMSHOE adventure will give you clear connections leading to new scenes, but you can still bog down play choosing between them.
Paradoxically, non-clues reinforce character competence. What seems at first to be a failure to gain information is actually an example of the investigators discerning that there is no information to be had. The distinction is subtle but important, and GMs should play up that, yes, the characters are good enough to know the difference.
For GMs, the non-clue can also help pacing. When telling the players that there is no information to be had, you can insert a silent (or not-so-silent) “yet.” If they uncover another clue somewhere else and come back, they may be able to learn more. This is called a “leveraged clue” in some GUMSHOE games.
For some clever ways to give out non-clues when using Interpersonal abilities, see the article 11 Things Functionaries Of The Gaean Reach Tell You While Impeding Your Hunt For Quandos Vorn on the Pelgrane site.