"El delito acusa" means "the crime itself accuses." In other words, the Spanish sentence is not the same the English sentence that precedes it. I cannot say for sure without the full context, but based on these two sentences alone, it appears that the author means: "Do not read this. Your 'criminal act' (the act of reading this despite the warning not to) will be self-evident (will accuse you, will give you away)."