I would counter by arguing that the truth can often be difficult to arrive at, even with a trial.
Please do not lose sight of the fact that Oswald along with his lawyer never had a chance to defend himself in court.
How many instances can you think of in which accused and arrested people were murdered while in custody? (And if you can think of any, were they supposed to happen?) I am not necessarily saying here Oswald did not do it, but the adversarial legal trial process can often be good at determining the facts (think Matlock if you must) and without it, the field is left open to speculation and polemics. Needless to say, the Oswald side of the story was never told, and opportunities were lost to investigate alternatives to the "lone nut" theory.
Have you checked out The Killing of a President by Groden? (Yes, Groden made a public professional error later in life, but that does not necessarily detract from facts independently established as in TKOAP).
I can be angry at a killer or killers, and the fact that two good people died that day, but I just consider it totally wrong and a waste of spiritual energy if I would be sidetracked into being made angry at the wrong person. On the contrary, I would strive to read everything I could about the matter, or at least as much as I had time to do, and make sure that both sides are well covered in my reading, before trying to come to any firm conclusions. And even so, the fact that there was never a trial means that there will always be a hole in the record with regards to this incident.
No, but I'm always interested in a good book on the subject. I'll put it on my list for my next trip to the library. Thank you very much for the suggestion.