How do you know the Mafia targeted the Smoke Monster?
The Mafia targeted someone who was being protected by a doctor because, the guy with the gun must be the Mafia and someone messed around with his gun, must've been the doc. The Smoke Monster aka Serial Killer targeted someone who was night immune and was looking to find a replacement, possibly the cult leader
On Night 2, the Serial Killer killed the Abhas and the Mafia killed the Spin
So going by your theory to find the Serial Killer, it must've been the person that FOS'ed or Lynched Abhas, nobody lynched or FOSed Abhas on Day 2 and therefore we can't guess the Serial Killer atm