"to figure out, investigate and discover," 1966, earlier "to suspect" (1953, police jargon), a slang shortening of suspect (v.). Related: Sussed.
Entries linking to suss
suspect v.
mid-15c., "imagine (someone) to be guilty on slight or no proof; hold to be uncertain, doubt, mistrust," from suspect (adj.) and in part from French suspecter or directly from Latin suspectare "to mistrust," frequentative of suspicere. As "imagine to exist, fancy as possible or likely," by 1540s. Related: Suspecting.