Detective O'Neil Murder Mystery: Death on the 101

Another book in the series of Detective O'Neil Murder Mysteries: This time, O'Neil is faced with a man murdered on a bus; the only passenger, yet he got on the bus without help, and sat at the rear. Nobody went near him during the entire ride, yet he had been stabbed when the driver found him dead at the end of the run. Who did it? Who managed to stab a man to death while not boarding the bus? O'Neil has help from a young probationary police constable who also happens to be the first police...