As in Dode stuck around and didn't follow Brendan to the library? So here's how I understand what happened:
Brendan found Emily's dead body and Dode was hiding in the tunnel at the time and saw Brendan there. Brendan then realizes someone's in the tunnel and chases after Dode. Dode punches him and is able to get away, and then he sticks around at the tunnel (maybe grieving over Emily). Later he sees Brendan come back and hide the body.
And although it seems weird that Dode would just be hiding in a tunnel I think I have an explanation for that. Perhaps he too was grieving over Emily's death and heard someone coming, so he decides to hide in the tunnel and see who's coming. Maybe he believes that Emily's killer is coming back to the scene of the crime.
Hopefully I finally got this right!