Headscratchers / Totally Killer

• How did Lauren know that Chris Dubasage was the new Sweet 16 Killer? His mask didn’t come off until he was alone with Jamie in the machine.
  • The ending journal doesn't specify that Lauren is keeping tabs on him because she knows he's meant to become a killer, just that she was keeping tabs on him. It could be that she was keeping tabs on him because he saw his dad die on the news then disappeared into obscurity, and so her concern is more for a former classmate who experienced a horrible trauma.
  • Partly due to the Timey-Wimey Ball, probably the older Lauren still remembers that the original timeline's Chris knocked out Amelia in order to use the time machine, even though she's now logically part of the new timeline where its version of Chris clearly did no such thing. Maybe the outdated memories for some characters are still partially retained if these characters are not drastically changed in the new timeline. But some can counter that Jamie STILL has a family to return back to when circumstances around how her parents hooked up had changed so radically. Of course, as the sheriff back in 1987 says so himself, time travel movies don't make sense, so one can argue in circles about this.
• Considering The Reveal, How did Doug get into the party in order to kill Tiffany? And how did he get back out again to meet Jamie at the door? Wouldn't he have been noticed? Randy was apparently acting as quasi-security to make sure no uninvited guests got through the front door.
  • Events are mixed up there. He met Jamie at the door before the killer got into the house, and right after that Jamie barges right back in and Doug follows her in. Randy was only intermittently acting as security but was otherwise happily enjoying the party, and in fact is shortly after accosting Jamie in the kitchen, giving Doug plenty of time to be creeping around and securing a good murder spot.
• Why did Chris bother chasing Jamie to the past? If anything, she would have ousted Doug as the killer, causing her to come back to the present believing that the killer that attacked her was Doug as well.
  • Finale spoilers: Chris's entire adult life is built around his investigation of the Sweet Sixteen Killer, which only has any audience momentum at all because it was never solved. He's aware Jamie is actively engaged in altering past events. If she prevents any of the girls' deaths, then the Sweet Sixteen murders become even less remarkable, and if she solves the case, then it's a historical anecdote that no longer needs investigation at all and his whole hustle goes away. Conversely, if she dies trying and/or antagonizes the killer to the point where he commits a couple of extra murders in the process, then it's like Chris says: the more famous the Sweet Sixteen killings become, the more famous Chris gets. He was already willing to commit at least one murder to grow the legend, so why not several more, especially since time travel means you don't need an alibi?
• How did Pam not ready weirdly when her kid grew up to look just like the psychic she knew? It’s one thing in back to the future, but in this movie, Pam’s daughter saves her life, and also convinces Pam she’s psychic! Am I missing something?
  • Considering that Pam only knew Jamie for a couple of days under stressful situations, she may not remember exactly what Jamie looked like, her mind subconsciously adjusting her recollections of Jamie to be bigger or more dramatic in some way based on the impression she made on Pam at the time. Add in that Pam is looking at 'Coilette' as a mother admiring her growing child and isn't actively looking for a reason to believe that the psychic who saved her life is actually her time-travelling daughter, and there are reasons she hasn't realised the truth.

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