Both Uses of

cunning
in
In Cold Blood

Headlined Clues are few in slaying of 4, the article, which was a follow-up of the previous day's initial announcement of the murders, ended with a summarizing paragraph: The investigators are left faced with a search for a killer or killers whose cunning is apparent if his (or their) motive is not.†
Chpt 2 *

cunning = good at achieving goals through cleverness and deception

And the radio, too-assuming that it was they who had stolen it, which was something Dewey still hesitated to do, for it appeared to him "ludicrously inconsistent" with the magnitude of the crime and the manifest cunning of the criminals, and "inconceivable" that these men had entered a house expecting to find a money-filled safe, and then, not finding it, had thought it expedient to slaughter the family for perhaps a few dollars and a small portable radio.†
Chpt 3

Definitions:

(1) (cunning as in: a cunning thief)
being good at achieving goals through cleverness -- and typically through deception as well (tricking others)
(2) (meaning too rare to warrant focus)
meaning too rare to warrant focus:

At one time, cunning was also used as a synonym for cute.