It is a shock to Gil to hear of his brother's death at the very least. When he learns that his brother was supposedly killed by a black man, he lashes out at Cal because he happens to be the only black man around. Gil isn't prejudiced like his family, but it's understandable that he would be upset and angry that his brother is dead. Of course, Gil doesn't really blame Cal, and later, Gil tries to convince his father not to avenge his brother's death himself, but to leave it to the police. Once Gil is over the shock of the news, he realizes how foolish he was to lash out at Cal.