Character mistake: When Scorpio hijacks the school bus near the end, he says something to the effect that they are going to take Sir Francis Drake Boulevard to the Santa Rosa Airport. Unfortunately, Sir Francis Drake Boulevard doesn't go anywhere near Santa Rosa, it heads west through Marin County and ends up near Pt. Reyes. They should have stayed on the highway and kept going north to get to Santa Rosa. (01:27:25)
Character mistake: The bus driver identifies herself as Marcella Platt, but after they get off the phone, the cop who checks her out calls her Priscilla Platt.
Answer: He certainly knew at the start, which is why he felt confident in pointing the gun at the (disarmed) robber and pulling the trigger. Harry knew he was bluffing, but passed it off so well the robber wasn't sure. At the end of the film, again, he knew he had one bullet left and wanted to bait Scorpio into attacking him, giving him an excuse to fire.