In the story, both of Steve's parents attend his trial. As to what his father thinks of his innocence or guilt, we will try to ascertain this by referring to the text.
Accordingly, the text does not clearly establish Steve's culpability in the shooting of Alguinaldo Nesbitt. We get the impression that he may have been a lookout for Bobo and King, but we can't be sure if this is what really happened.
In her closing statements, the assistant district attorney, Sandra Petrocelli, argues that Steve is guilty, even if he didn't pull the trigger. She claims that his participation in scouting out the store ensures the certitude of his guilt in any rational person's eyes. Petrocelli thinks that Steve should be held accountable for his part in the crime, regardless of whether he participated in the killing or not. Steve's denial of guilt in the affair corresponds to his diary entry that 'he didn't do nothing.'
Steve is acquitted, but the gist of Petrocelli's arguments stand. Perhaps this is why even Steve's attorney, Ms. O'Brien, refuses to return his hug after he is found not guilty by the court. The text tells us that she stiffens when Steve approaches her for a hug and that she moves away from him. Perhaps she is not sure whether she has just helped to secure a guilty criminal's freedom or assisted in freeing an innocent by-stander. For that matter, Steve's father is just as ambivalent about Steve's guilt as O'Brien. Let's take a look at the text:
After the trial, my father, with tears in his eyes, held me close and said that he was thankful that I did not have to go to jail. He moved away, and the distance between us seemed to grow bigger and bigger. I understand the distance. My father is no longer sure of who I am. He doesn't understand me even knowing people like King or Bobo or Osvaldo. He wonders what else he doesn't know.
Like Ms. O'Brien, Steve's father appears ambivalent about Steve's acquittal. Because the text does not explicitly establish Steve's guilt (and Steve himself does not clearly admit it), we can only guess at the thoughts Steve's father has towards him. At this point, we know from the paragraph above that Steve's father feels blind-sided by these new revelations about Steve's extra-curricular activities and his acquaintance with shady characters. These are stunning and not especially pleasant revelations for a father to have about his son.
The statement 'He wonders what else he doesn't know' clearly illustrates that Steve's father is troubled about the possibility of his son's involvement in the homicide. However, at this point, he is relieved beyond measure that his son is a free man, and despite any reservations, he will welcome his son back home.