The pattern here is like verses 27-28: "You have heard that it was said, ‘You shall not commit adultery.’ But I say to you that everyone who looks at a woman with lustful intent has already committed adultery with her in his heart."
The message is that anger is as bad as murder. I don't think the three-step sequence "everyone who is angry with his brother will be liable to judgement; whoever insults his brother will be liable to the council; and whoever says, ‘You fool!’ will be liable to the hell of fire" is three separate sins, but three ways of expressing the seriousness of anger.
Eugeme Petersen's The Message gets the basic idea across, I think: "You're familiar with the command to the ancients, 'Do not murder.' I'm telling you that anyone who is so much as angry with a brother or sister is guilty of murder. Carelessly call a brother 'idiot!' and you just might find yourself hauled into court. Thoughtlessly yell 'stupid!' at a sister and you are on the brink of hellfire. The simple moral fact is that words kill."
Matthew Henry's commentary says: "The Jewish teachers had taught, that nothing except actual murder was forbidden by the sixth commandment. Thus they explained away its spiritual meaning. Christ showed the full meaning of this commandment; according to which we must be judged hereafter, and therefore ought to be ruled now. All rash anger is heart murder. By our brother, here, we are to understand any person, though ever so much below us, for we are all made of one blood. 'Raca,' is a scornful word, and comes from pride: 'Thou fool,' is a spiteful word, and comes from hatred. Malicious slanders and censures are poison that kills secretly and slowly. Christ told them that how light soever they made of these sins, they would certainly be called into judgment for them. We ought carefully to preserve Christian love and peace with all our brethren; and if at any time there is a quarrel, we should confess our fault, humble ourselves to our brother, making or offering satisfaction for wrong done in word or deed: and we should do this quickly..."
And what makes you think the Aramaic "raca" is used in Proverbs? The book of Proverbs is Hebrew, not Aramaic.
