How can you be sure it wasn't a lag spike (on his side) ?
I happens sometimes to me because my ISP is trash.

Hi @TeNoR,
It is hard to tell if this is a hack, a bug or "real" lag.

I was played 2 games versus him (and I have only this record), he used covers and than use hack to kill players (you can't see and hear shooting animations, only death screen after). His scores was 10/1. If you see hacker at one place and try killing him, you will be dead and he will be die only after 2-5 second... In the video you can see smooth animation without lags after kill (he don't use hack always). I increasingly meet similar cases, it's really big hole in the anticheat system.

Like hack from Arma 3 (lag switch) https://youtu.be/nMIocPn9JZ8?t=30 (thanks Crayon DeCire, for info)

This again happened, hacker name: Captain Nost (ping in game 17)
https://youtu.be/7rKVXGUEf1g