The Randolph Scott character claims to be interested in seeing justice done by taking a young man in to be hanged for a senseless murder; yet, it turns out he has ulterior motives. We see the possibility between a person's true motives and the perfectly legitimate moral justifications he can give to obfuscate his true intentions.
The Pernell Roberts character wants to take the young guy in as well, but his motives are also less than direct.
Everybody wants justice, but they all want it for different reasons.