Didnt the Leprechaun cheat by brekaing the rules of giving up his gold?

I know he is psychotic, but witness his shining the shoes. He is bound by some code to follow a certain way of doing things. I was always told that if you caught a Leprechaun fair and square, he had to give up his pot of gold. isnt that the law of the wee folk? I never heard any Irish stories from my wife's Irish Grandmother about the Leps being vindictive. Yes it makes the story scary but still I wonder if there is something else in the lore that would allow him to kill and maim to retrieve the gold the code says he must give up.

He must have been an outcast, the Gollum of Leprechauns to refuse to honor ancients traditions thats all I can see. Thats why he was so distorted in visage like Dorian Grays painting. From Smeagol to Gollum.