1940s American English police jargon shortening of perpetrator (as in perp walk).
Entries linking to perp
perpetrator n.
1560s, "one who commits or has committed," literally "the one who did it" (in English usually an evil act), from Late Latin perpetrator, agent noun from past-participle stem of perpetrare "to perform, to accomplish" (see perpetrate). Fem. forms are perpetratress (1811, of Nero's poisoner Locusta); perpetratrix (1862, in reference to Charlotte Corday).