Why did Locke kill Pacthy?
I think that Patchy knew a dark serect about locke, Locke din't want anyone to know about it so he killed him.

How does pacthy know Locke?
The others have a book about jacks life. SO they know about his past life.
They dont know kate or sayid.
So how do they know stuff about locke.
In the peview for the next episode Ben knows that Locke was in a weelchair so maybe pacthy gave him this information.

In season 3 episode 7 it shows how Juliet joined the others and it shows that they knew a lot about her.
So maybe they know a lot about JAck and Locke because they wanted them to come to the island as a other like the way Juliet did.