Threatened by a player who wants to kill my family.

Hello, i got threatened in the last match by an ADC player because he died often and i was support and could not help to prevent that twice. After i warned him that i will leave lane and support someone else if he didn't stop flaming and insulting me, i finally left lane and went to top because the toplaner was afk. The ADC then threatened me to kill my father and gun him down. I want to report this severe case not just ingame cause i know that a lot of the ban system is automated and maybe even file a lawsuit against him, what do i have to do? Please Riot respond.
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