During the course of Insomnia Ellie is given the task of investigating the death of Det. Eckhart, who is supposed to have been shot by the killer, but who we know was shot by his partner Det. Dormer. When Ellie has finished her report she hands it to Det. Dormer to sign it. Yet he rejects it and says she should double check it and make sure everything is correct (forgive me for not quoting it word-accurate):
Ellie: My report, it's finished. You only have to read and sign it. It basically explians itself all by itself. Looking forward to working with you again, we got more important things to do here than this paper work.
Dormer (retreating the pen): A man is dead Ellie, that is important. Make sure of all the facts before handing this in, your name is on this report.
But right before reading that report he went out of his way to cover his guilt in Eckhart's death and foist it on the killer (e.g. by hiding the gun and substituting the bullets). So why would he now urge Ellie to investigate further if he could just have had it filed away by simply signing her report? (And indeed she finds contradictions between his statements and the evidences after looking further.)