Rengar bonetooth not stacking?

I'm not fully sure how it works but I'm pretty sure I was supposed to get it in this scenario; I ulted when and were pushing my turret, Jax was low and I went for him, he flashes away and Akali kills me, but, the turret manages to get Jax after flashng away and he dies. Then, I don't get the bonetooth??? I had already gotten it on Akali minutes earlier so I don't think it was cooldown related. Is it because I killed hm after I died? (The turret gave me the kill).