MAJOR SPOILER WARNING
[color:#C0D3F2]Before Matt Damon killed Jack Nicholson, Nicholson told him that he only gives up people who are going down anyway, and nobody knows about him.
Later, during the elevator incident, the 2nd mole (who appears out of nowhere btw) shoots Leo and apparently knew that Matt worked for Nicholson (but noone else knew).
This doesn't make sense, and the 2nd mole is obviously a deus ex machina to save the plot from falling apart.
(highlight to read)