Aish.com has an article on the etymology of the word genocide:
The man who coined the term ‘genocide’ was fighting to make it an international crime decades before the Nazis rose to power. … Lemkin entered the University of Lvov in 1920 and majored in philosophy, hoping to find answers to his questions. While he was there, an incident occurred that greatly altered his direction. In 1915 he was shocked to read about the massive slaughter of Armenians by the Ottoman Turkish Empire resulting in the massacre of over a million innocent people. Six years later, a young Armenian assassinated the Turkish Chief of Police in retaliation. “That is for my mother,” he said, before giving himself over to the police. Lemkin asked one of his professors why the Chief of Police had not been brought to justice for the grotesque perpetrations that he sanctioned against the Armenian people. The professor responded that he had not transgressed any international law and that it was an impingement of a nation’s sovereignty to interfere with their internal affairs. He compared it to a farmer who has a right to slaughter his own chickens whenever he wishes.
This time he decided that the only way to find an answer was to become an expert in international law.