In season 3 of Game of Thrones, it was Locke who

>! cut off Jaime Lannister's hand.

Locke is one of the men under the command of Roose Bolton. How did he end up in the Night's Watch?

Also, in S04E05, Locke tries to
>! abduct Bran Stark when he comes to know of his identity  

But since in the same episode  
>! He is killed by Hodor through Bran  

What was his plan exactly?