Unanswered questions about The Killing, Series 1

[Sinkingfeeling]

OK, a bit late I know, but have just downloaded series one and finished watching it. Sarah Lund, what a woman. Bit confused though - can anyone help me out?

Was Troels Hartmann completely uninvolved in the murder? Why did he get rid of Rie at the end? How did Vagn gain access to the party's flat? How did he get hold of Hartmann's car keys?

I'm probably being a bit thick but have been mulling it over all day ...

ok, I'll try

• troels hartman uninvolved
• vagn had access because of a move of party leaflets to the school
• car keys don't quite remember, but had something to do with the driver

I've just finished watching it too - wasn't it brilliant? Twenty glorious hours of gripping TV. Can't wait to watch the second series.
To clear up the question of the car keys I think Hartman left them at the flat when he went off to the cottage in a taxi for the suicide attempt - and Vagn would have picked them up from there.
But I've got some unanswered questions too:
What about the other missing person files?
Why didn't Bremer give the picture of Hartman and Nana to the police?
Why was Brix protecting City Hall?