Spoilers
I could've put Deb in there as well just to show when her apartment was accessible but I didn't think it necessary. Apparently, Dexter's old apartment is really easy to break into. As was shown by Rudy in season 1, now shown by Arthur in Season 4.
Here's the timeline, with some notes. The text in script is the sketchy part that isn't shown. We are just supposed to assume the leaps made were obvious after knowing the final result.
After searching around the webs a little, some people are saying that Arthur went to Dexter's old (Deb's) apartment, the night before. I didn't think so when I watched it, but that would make a lot of sense. He would've had a lot more time to prepare. Also, he might've found the file that said who Dexter's mom was, and that would've given him the opportunity to set up the kill to reflect Dexter's past. Like I said, when I watched it, it seemed like Arthur went to Deb's in the morning, which meant he did a ton of stuff. Look at his timeline, he's doing something every second.
If Arthur goes the night before and finds Dex's address, that clears up a major problem. But some other things still bother me. Why doesn't Dexter check his phone all day? He always takes calls from Rita even if
he's in a car chase. He would want to know how the flight went and that she was ok. Since there is a serial killer that's mad at him, you think he'd want to be certain. It's possible he would've checked it so late that Rita was already dead, but it would've been before the end of the day.
Rita has to come back from the airport pretty quickly. After handing your bags in, you go through security. It wouldn't take long for her to realize she didn't have her ID. I think she would've had enough time to go home and then return to the airport and still make her flight. Her luggage would've been loaded already. If she was going home to return quickly to the airport, the taxi would've waited outside while she ran in to grab her ID. That would've made it pretty tough for Arthur. Arthur could've pretended to be Rita's husband and told the taxi to leave, however Arthur wouldn't have had the money to pay the taxi. And Rita probably wouldn't have paid him yet, because she will just pay him when they got back to the airport.
I can't even believe she went on a plane with a child that young. From the center of Miami, the Florida keys is about 3 hours. The airport is 30 mins. Try packing for an infant and fitting it on a plane. Diapers, food, carseat, bathtub, clothes, that's a lot to bring on a plane by yourself. She must breast feed and bathe him in the sink to save space.
After Arthur kills Rita he is wearing the same clothes as before. I thought this was a problem because he would've gotten some blood on him. But he usually gets naked for his kills, so that doesn't matter. However, that does add more things to his timeline. He got there before Rita in order to get undressed and he might've gotten a shower at Dexter's house afterward as well.
Lastly, how does Arthur realize that Dexter doesn't live in his old apartment? He sees some mail that has Deb's name. How does he immediately know that's not Dexter's wife? I would've been much happier with an ending where Deb died. At least the scene where he went to her apt was shown. Many of the other scenes are not shown, which makes them less believable. I felt like I was watching No Country for Old Men.
So maybe the killer wasn't Arthur.
(there's something on the wing!)
I think the real killer was...
