Relapse S rank coop

I've been trying to s rank this mission for a week and I keep failing with the AI team. Every time I get really close, but there's always one guy spraying 7,62 bullets from nowhere that kills me or one of the squad. I tried the grenade launcher and ended up killing suspects with It.. the pepper rifle is very weak and the beanbag shotgun is too slow. Can anyone join me to try to beat this b*tch? It is the last one i'm missing and by far the most annoying