There might be a rather humorous explanation for why the Whistling Man chose to outright kill Murphy instead of just simply beating him up and leaving. Knowing how fraudulent Master Robbie's tapes are, there's a possibility during the fight that Murphy ended up groping and feeling the killer's body, and greatly pissing them off. This could also be the reason that Murphy was so convinced that the Whistling Man was male...depending on where he grabbed.
Though the beginning tutorial scene may have just served to be a creepy opener that introduced us to the Whistling Man, why were they there in the first place? Considering Henry was at the sheriff's office at the same time, that had to have been Marie. If she was there at that time, she was possibly setting up for when she got Forrest to go outside and retrieve the disk for "Long Ride Home."
This one is kinda combined with Fridge Horror, but one has to wonder how Marie even knew where her victims were gonna be tonight, such as Euguene going to the Maize Maze for his date. However, when you remember that Clive was originally trying to piece together who any potential victims were gonna be, it could be likely that Marie managed to get Clive's notes after killing him.
If you pay attention to the context clues within the game, you can actually figure out which killer is attacking the callers throughout the night.
For starters, as mentioned in Henry's character folder, all of the unavoidable deaths in the game were caused by Marie. This means that Sheriff Matthew and Clive were killed by Marie. Coincidentally, since Martinez ends up being attacked by the Whistling Man right after Clive gets killed, that means that the person who later goes to kill Martinez would have to be Henry.
Henry obviously is the one that shows up to the Gallows Report and tries to kill Maurice, since Marie tells Forrest that she didn't appreciate them locking her son up if they actually succeed, which means Marie must've been the one that targeted Sandra.
It's never explicitly stated who attacked Virginia, but it most likely was Henry. We know for a fact that Marie is the one that attacked Eugene in the Maize Maze, since she can admit to it in the endgame if you bring it up. The Maize Maze is located at the top of the map in Giblet Field, while Virginia would most likely live at the bottom of the map in between Chalupracaba, Grilling Spree, and Ponti's Pizza. Very little time passes in between Virginia being saved by the killer and Eugene calling into KFAM, so it would've been absolutely impossible for Marie herself to have stalked Virginia and then make her way to the Maize Maze.
Henry is obviously the one that attacks and tries to kill Murphy since it gets revealed at the climax of the game (if you saved Murphy).
Since it's established all of the unavoidable deaths are from Marie, that means that she's the one who brutally kills Jimmy and therefore is the one that attacks Carrie's friends.
It's not explicitly stated who's the one that tried to blow up the gas station with Chuck Brody in it, but it's very likely that Henry did it considering how he went about dealing with Murphy.
The final victims, Roller Ricky and Jason, of course were obviously attacked by Marie.
As the end credits are rolling, you suddenly are in the position of an unknown person in what seems to be a hideout and on the the wall is pictures of various characters throughout the game, and they'll have X's on their picture if they're dead. Forrest himself is one of the pictures on the wall and considering he is able to die, you're likely not controlling him. And we know Clive is dead at this point, while Henry was apprehended by the police, could this be a sign that Marie might've survived?
Going off of the above, if Marie did indeed survive, there's a pretty good chance she's not done. Considering both her and Henry have spent the entire night hunting people, she would've only had time to mark her victims dead after the events of the game. This could imply that (should Forrest, Peggy, and any of the other callers survive) she's gonna plot to kill them all after recovering.
Assuming Marie herself is the one that put up the images of the characters to mark off whoever she killed, this becomes even more horrifying because it implies that those such as Forrest, Murphy, and all of Carrie's friends were always intended to be targets, despite having absolutely nothing to do with them or what happened to George.
Given that we know Revenge by Proxy isn't off the tables for Marie, and that even insulting and/or calling out the killer can put you on their hit list, there's a good chance many of their victims from out of town were innocent people unfortunate enough to either be related to someone or were just killed from simply saying the wrong thing.
While it might be very unlikely considering her concern for him when the cops came, one can only wonder if Marie ever harbored any negative feelings towards Henry or even considered murdering him at least at one point in time. Considering her... mental state and her reasoning for killing her own sister, it wouldn't be too unlikely that Marie may have blamed Henry's existence for her getting kicked out of her home. And even if she never did blame Henry and genuinely always loved him, considering how unstable she is and her actions towards her own sister, who's to say she wouldn't do anything to her own child if he were to ever get cold feet about what they're doing?
Teddy Gallows Jr. gets a terrible future no matter what Forrest (or the Player) does, and if it weren't for the fact he's an arrogant jackoff, you'd feel bad for him. Either he ends up dead by the vengeful girlfriend of his former friend, or he survives but loses any chance of getting elected after admitting to accidentally killing George on the radio, but it gets worse with the latter. Teddy's likely in big trouble with the police because he confessed on live air while they were listening that he did manslaughter and had his dad and Clive cover it up. Not becoming Gallows Creek's mayor is the least of his worries.
Ant Williams and Rebecca Allen were both suspected of being potential targets of the Whistling Man, however they never make any appearances in the game, although this is justified in Rebecca's case since she had left Gallows Creek before the start of the game. However, considering that we know Marie and Henry had been busy and killed plenty of people before moving in to Gallows Creek, there might be a chance they got her. Furthermore, Forrest does propose the possibility of the victims not making it to the phone before getting killed, so there's also a chance Ant may have gotten Killed Offscreen, likely during the period of time Forrest went to look for Marie's song or right at the moment he said then when he was investigating Clive's recordings.
