I certainly think that Forster makes the argument that it would have been difficult for Aziz to receive a fair trial. The idea of "the machinery had already started" brings to light that Adela's accusations carry so much political and social weight to them that had the case continued, it would have been nearly impossible for Aziz to have a fair trial. Yet, I think that this extends to a larger issue than Aziz's trial. In my mind, Forster seems to be casting a wide enough net to assert that anyone trapped in the clash of cultures in the time period was unable to fully perceive anyone's "guilt" or "innocence." Take Aziz, for example. After the trial, Aziz holds a great deal of resentment towards Fielding for little valid reason. Aziz allows himself to be colored by the lens of cultural perception and racial bias in presuming only the worst of Fielding. The ending seems to indicate that while both men might rise beyond their social stratification, the ability to view people as outside of their cultures is something that is not ready to happen as of yet. In this light, Forster is asserting that few can ever be "innocent" or "guilty" in such a condition of cultural clash.
Yes, that is very possible and yet sanctiful. But the myrobility may cohenside with the prejudice of British culture. Dr. Aziz may be innocent but he is still foletious his battles of torjance and torchire account for the rencklest of the British prejudice.
Hope that helped. :)