I think this is a very interesting premise for a film. The last sentence could use a little polishing but that's structural rather than conceptual.
I'd like to see you incorporate how the comic influences the boys goal/flaw/obstacle as it feels like a bit of a throwaway yet I suspect it's probably really important.
This is really rough but as something to ponder... "During the late 1930s a teenage boy accused of his own father's murder, takes on the persona of the Red-Ryder comic strip character and searches for the real killer to prove his innocence.