Running into trouble

The only way I can get my mind off of Barbara's murder is to go running. Today during my run I found myself on Barbara's street, jogging towards her house. As I got closer, I saw that someone was standing on the sidewalk across from her house. As I came closer still, I recognized the person as Gus, an erratic man of no fixed address who spent a couple of month's on Barbara's sofa. After she told him he needed to move on, he became furious with her. Now I wonder: Was he mad enough to kill her?