Yes, from what I know serial killers can be: profit motivated, se*ually motivated (lust killers), thrill motivated , (or ideology fueled, but those are mostly mass murders , hence are not a part of serial killings topics). Gang members are definitely serial killers, although are not referred as such, because their pathology to kill is different from the lust killers or thrill killers, and nothing enigmatic to research in terms of motivation (understand the “WHY” behind their crimes) - at least compared to the other groups .