Zack targeted anyone who looks happy, regardless of gender or age. From the flashbacks and article of one of his murders, it is shown that Zack killed his victims in back alleys or secluded environments where less people pass by, which implies that Zack either lured his victim to an alleyway or waited until his victim is in a place where there are the least or no people passing by during the night. Zack would usually give his victims 3 seconds to try to run away.