Hello again, here's another list of doubts!

1) I just came across an expression I don't understand. What does
C.I. stand for? The situation is, a plainclothes detective has a
"punk c.i." that allows him into the drug dealers world, so I suppose
it's ome kind of informer...

2) Briscoe and Green are looking for a suspect, and Briscoe says:
"Twelfth time's a charm". I have no clue as to what that means...
Does that mean after 12 tries to get the right person they finally
got it?

Nothing really important, as you can see -but they bug me anyway! :-)

Alberto