In Pretty Little Liars Season 2 Summer Finale:What was Jenna and Garret talking about?(For those who haven't seen the finale, this could be a spoiler..)

In the scene where Jenna came to the police station..What where they talking about? Did they kill Alison? Where they the ones who set the girls up? They seemed so happy about what's happening to the girls. And it was Garrett who roubou page 5 of the autopsy denunciar so they could get rid of the evidence linking them to the crime? It wasn't said if they were really "A." But it seems to be implied that they are....
And oh! when they mentioned Jason, they said Jason figured out that it wasn't him who killed Ally, then what was the seguinte line that they said???
I'm just so confused!!!