I had always thought there was a possible robbery motive in this somewhere (not necessarily Joran or Stephany robbing each other).

The other thing that is still bothering me is Elton Garcia telling others that they were missing and might have been kidnapped. What did he know and how did he come to that conclusion? "Kidnapped" would mean there is somebody else involved here.

I'm still interpreting Stephany's gait and demeanor in the lobby as "acting". She is on some kind of mission, or under some kind of stress. She is not behaving naturally. That is what brought me to my earlier conclusion she was doing some free-lance investigating.

If he told the Chilean police that he knew she "wasn't interested in boys", he likely knew that before they got to the room, and I think that fairly well washes out the idea that he killed her because she wouldn't have sex with him.

Whether or not Van Der Sloot was googled is easily answerable.... they have his computer and can see if a search was done during the time he came back from getting the coffee and leaving the room.

Later, having apparently decided to keep their kidnapping to themselves, they returned to the hotel.  Joran and Stephany went to his room where they found the same mysterious strangers.  They were no longer dressed as police officers (having apparently gone home and changed clothes).  Apparently, it hadn't occurred to the "policemen" to try and force Joran and Stephany to give them money whilst they were in the car.   Upon reflection, the "policemen" realized this was a mistake and went to Joran's hotel room to wait for the couple to return.   They beat Stephany and she hit her head and died.   Now, having murdered the daughter of a prominent local businessman, the "police officers" decided not to beat Joran until he gave them money and instead they left him---the only witness to their brutal killing--- unharmed and free to call the police, the hotel manager, the Dutch embassy, or his mother.  

For purposes of this story, we won't question how blood got on his clothing (although it apparently did) or why he didn't summon help for his friend.  One should never demand an explanation from a professional gambler and international man of mystery.  Let's just accept that he gathers together his belongings and goes to Chile (where he decides that the best thing to do is just keep quiet about the whole murder thing).  No doubt his reason for staying silent once in the apparent safety of Chile was that the "policemen" told him they were from a powerful secret organization (maybe SMERSH or THRUSH or maybe they worked for the same Columbian drug dealers that actually murdered Nicole Simpson).  Anyway, he's absolutely terrified that they'll murder him or his family or his dog---again, as a professional gambler and international man of mystery he knows that the thing to do is to stay silent about the involvement of these men forever.  He will take the truth with him to his grave!  Or he will puke his guts out to the Chilean police, apparently the moment they arrest him.  It may be that there are some parts of this that he hasn't remembered yet----probably the part about his family being in danger---but I'm sure he will soon.

For what's it worth, I find both the Chilean story and the current story about equally silly.   Since we're all wildly guessing anyway, here's mine:

They meet playing poker.  Long hours and high stress.  They're both tired.  He suggests they go to his room to rest.  They talk.  They relax.  He thinks he's doing well, maybe going to get lucky.  He believes in his charming self.   He suggests that he get some coffee and bread from across the street.

When he returns, they talk some more. His confidence grows, he is sure he's going to get lucky---after all, he knows that he is charming and irresistible to women. Always has been. He makes his move.  She laughs at him, tells him that not only does she prefer batting for the other team, she wouldn't screw him if he were the last man on Earth.  He's tired and stressed----the stress is tremendous, not only from the poker game but also because he knows that the FBI is closing in on him. Everything is falling apart.  He's on his own, nobody influential to protect him now.  

He's always been high strung but now he's really on edge.  The one thing he's always known is that he's irresistible to women.  He can't take being laughed at by this lesbian.  He snaps.  He gives her what for.  But maybe he hits her too hard; maybe she hits her head as she falls.  From the time he returns with coffee to the time he kills Stephany is only a matter of a few minutes.  He panics and flees.

That's the direction I think I'd be going in if I were the prosecuting attorney (or examining magistrate or whatever they've got down there).  Seems to account for most of the facts. Maybe some problems with the time-line but it's pretty clear and simple----doesn't require silly leaps of logic about what's on his computer, etc.  

including whether his father had helped him hide the body.