Hi Sinead,

Some more reference would probably shine some light on the specific use in this instance (is the witness a mere onlooker? has he/she been harmed in any way by that fraud?), but one possibility, given the context of lawbreaking, could be that "cosquilleo/cosquillas" is here being used with the figurative meaning of "concern, worry, anxiety-like feelings". A common Spanish expression where this is seen is "tener un cosquilleo/cosquillas en el estómago", meaning that you're quite worried/anxious about something. If this is correct, the fact that he replies "Hasta hoy", and both of them laugh, could be a sign of relief that the "cosquilleo" (concerns) has been dispelled today, by virtue of the agent.