Multiple times I was in good position ready to flank and then there he is peeking me somehow. Didn't get any good footage because the server died right as I started speccing but it looks like his numbers tell the story. 

https://i.imgur.com/Dzfrx7L.png

A HS% of 53 with an LMG with over 200 kills is pretty telling. It's possible if you just look for people prone and specifically go for headshots but then your KPM would be way low, below 1 and he has a high KPM and super high HS%. I think it's telling unless he's a pro competitive cs player. 

And with 2 of his 4 guns, he was the exact same HS% of 33.33%. Seems like he set his bot to headshot at that rate imo.

You can see exactly when he started cheating. Here is his set of games a month ago. Then, here is his next set of games, 7 days ago, notice how he goes from under 1 KDR to about 5.

^^Moved it up