Translation of "Assassin" in Japanese

A rarely-seen assassin...

‎姿を見せない殺し屋

When an assassin opened fire with  a home-made, multi-barrelled gun:  

暗殺者が自家製の多銃身の銃で発砲したとき

But he's not destined for a peaceful end. There's a nocturnal assassin down here.

‎だが安らかな ‎最期にはならない ‎地上には捕食者がいる