In Anthony Ascott's giallo The Case of the Bloody Iris an otherwise innocuous seeming old lady is made into a suspect by the expedient of having her purchase of what are described as “horror comics” - fumetti neri, including the fictitious title Killerman - from an edicola.
One interesting thing here is how the transgressive aspect of such titles, including the real-world Diabolik, Kriminal, Sadistik and Satanik, seems to be signalled in the Italian at the level of their titular protagonists, the letter K being one that is foreign – with all the associated connotations of otherness, potential danger etc. – to the Italian alphabet.
The function of the K, then, seems akin to that of the X in more familiar English-language / American comics like X-Men. The difference is that whereas X-Men present us with the world from the perspective of the outsider (i.e. the mutant) who fights heroically for a society that fears and rejects them on account of their difference, in their fumetti counterparts the world is presented from the perspective of an outsider (i.e. the master criminal) who revels in their rejection of society and its norms.