In this sentence from 龍が如く極, localized title 'Yakuza Kiwami', (spoilers)
Nishikiyama says 堂島組長殺ったのは…この俺だ！
where 殺った is pronounced as やった. I checked a kanji dictionary but didn't see a kunyomi of や(る) listed for 殺. Is writing やる as 殺る a slang usage? What's the difference in nuance between saying 殺した vs 殺った?