I heard the following from Rabbi Yisrael Dovid Shlesinger shlita (from Monsey): Yehuda said, "What gain will we have if kill our brother and hide his blood?" Anything a person does that he feels the need to hide afterward, shows that he realizes maybe he should not have done it. So Yehuda said, "Why kill him and hide the facts later? If killing him is the right thing to do, then we should be able to face up to it and say, "yes, we killed him because he deserved it". If we can't face up to it, then our motives are suspect."