Consider the city of refuge law in Deuteronomy 19:
Here is the law concerning a case of someone who kills a person and flees there to save his life, having killed his neighbor accidentally without previously hating him: If he goes into the forest with his neighbor to cut timber, and his hand swings the ax to chop down a tree, but the blade flies off the handle and strikes his neighbor so that he dies, that person may flee to one of these cities and live. Otherwise, the avenger of blood in the heat of his anger might pursue the one who committed manslaughter, overtake him because the distance is great, and strike him dead. yet he did not deserve to die, since he did not previously hate his neighbor. [Deuteronomy 19:4-6, HCSB]
Compare Jesus' words in the Sermon on the Mount:
You have heard that it was said to our ancestorys, Do not murder, and whoever murders will be subject to judgment. But I tell you, everyone who says to his brother, 'Fool!' will be subject to the Sanhedrin. But whoever says, 'You moron!' will be subject to hellfire. [Matthew 6:21-22, HCSB]
Jesus' sequence of "You've heard that it is said" statements and their corresponding "But I say" statements are sometimes taken to be revisions of the Torah or at least revelations of the hidden meaning behind the Torah, which readers couldn't have seen very easily without his aid. Not so. When he refers to the spirit of the law, he doesn't mean just some hard-to-see intent. He means the basic fundamental principles that undergird the specific teachings, and these are usually explicitly taught clearly within the Torah, some of them over and over again.
I just noticed this particular statement yesterday, but it's pretty clear in the Deuteronomy passage that the difference between the murderer and the manslaughterer is that the murderer hates their neighbor. The reason the manslaughterer doesn't deserve death (and by implication the reason the murderer does) is that the manslaughterer doesn't hate (and the murderer does). So it's actually hate, in Deuteronomy 19, deserves death. When Jesus says that anyone who hates deserves hellfire and judgment, he's not going deeper than the Torah's own criterion, which is the heart attitude. There are probably lots of cases of this kind of thing, but this particular one struck me yesterday when reading Deuteronomy 19. I don't think I'd ever noticed it before.