Although one may initially assume that when Doug goes back in time he is still operating in the same timeline he left, this is not the case. This is evidenced by the fact that the movie shows Doug travel from a timeline where the ferry explodes to a timeline where the ferry explosion is prevented. There are actually 4 individual timelines in the story, only in the last of which Doug succeeds in preventing the bombing. The movie shows the events after the explosion in Timeline 3 and before the explosion in Timeline 4.
In Timeline 1 Carrol uses his original car to blow up the ferry. Claire is not harmed. Doug sends the notenote They don't know about Claire, so they don't track down Carrol via his phone call to Claire. Then how do they know what to write in the note, i.e. when and where to find Carrol? Probably because they simply see him while watching normal security-camera footage from the dock and find his night visit to the dock suspicious. back in time, creating Timeline 2. note Without knowing Claire, does Doug go back in time to Timeline 2 to try to save the ferry passengers? It doesn't seem to matter: If he does, he doesn't manage to prevent the ferry explosion and end the branching of timelines. Claire is not on the ferry to help him as in Timeline 4, and his confrontation with Carroll goes differently than in Timeline 4 anyway because he doesn't stop by Claire's house.
Timeline 2: Like in the movie (Timeline 4, where Doug's partner goes alone and Carroll ruins his car) or via a different mechanismnote Without Claire's involvement in Timeline 1, the investigation there goes very differently than in the movie (Timeline 3), so the note probably arrives in Timeline 2 at a different time than in the movie (Timeline 4). Via the same mechanism as in the movie (Timeline 4, where Doug's partner goes alone and Carroll ruins the car) or a different mechanism (for example, several policemen stake out Carroll at the dock and see his car, scaring him away and making him want to switch cars to not get recognized by his car), the note causes Carroll to get Claire's car., the note causes Carroll to get Claire's car. Thus Carrol kidnaps Claire, kills her at the warehouse, and uses her car to blow up the ferry. Claire's body is not wearing a red dress and there is no message for Doug on the fridge. Doug nonetheless goes back in time to Timeline 3.
In Timeline 3 Future!Doug steals the ambulance, crashes into the warehouse and rescues Claire. They go to Claire's apartment, she changes into the red dress and he leaves the fridge message. However he then makes the fatal mistake of leaving Claire at the apartment—Carrol, knowing where she lives, shows up, burns her alive and cuts off her fingers. Future!Doug is unable to stop the ferry explosion and dies in it. The events of the movie then begin here.
In Timeline 4 Future!Doug does everything the previous Doug did last time, except this Doug had seen his own bloody clothes in the previous timeline, so he recognizes them, realizes that so far he did everything the same as in the previous timeline where Claire died, i.e. that she is in danger by staying at home. So he takes Claire with him to the ferry. They are successful in preventing the bomb from going off on the ferry but Future!Doug is killed. Claire then encounters the Doug from this timeline.
At the end of the movie, Larry's still dead, but nobody in the world knows it, because the only people who knew about his death are either dead or in another timeline. We also know that he won't be missed for some time, thanks to his conveniently timed vacation. This may lead some people in that timeline to eventually wonder "whatever happened to that guy?"
But the bomber would be identified relatively quickly, thanks to Claire, and his compound searched. This would lead authorities to find Larry's remains. They'd also find Larry's DNA inside the Blazer and the slugs from his service weapon. The only mystery would be how he ended up dead.
That mystery might be quickly solved with the "Snow White" team investigating whether Carroll had accomplices, or investigating whom (someone whose description matches Larry's partner Doug) the five cops in the end saw in the car on the ferry with Claire, or investigating because Claire's story may be weird and may or may not include how Doug claimed to be part of a "special surveillance unit", could foresee answering-machine messages and Carroll's actions, disappeared in the explosion, and then "reappeared" with different memories. The remaining mystery for the "Snow White" team is what happened in the previous timelines.
