Sorry I’m just now getting around to this, but there are a few important things to keep in mind. First, it’s almost impossible to make a game about a serial killer without including some level of violence. That said, how you present it matters a lot. The visual style plays a big role, something like PSX-style graphics is generally fine, but going for ultra realistic, hyper-detailed gore (like Unreal Engine 5 realism) is not acceptable.
Elements like dismemberment can be included and won’t automatically disqualify your game, but excessive or over the top violence will not be well received by the judges and could hurt your chance.