Not looking suspicious is all well and good, but impostors still need to find the opportunity to kill other people. This means prolonging their time on the map so they can’t leave and actively putting up barriers that will enable impostors to kill more easily.
In practice, this means sabotaging whenever possible and shutting doors before killing someone off. These will provide an impostor several opportunities to off one of their targets with a higher chance of not getting caught. Taking out the lights, in particular, can be used to great effect if there only a few players left to eliminate. Similarly, something as simple as shutting the door before killing an opponent will allow an impostor player an additional few seconds to make a speedy escape if they need to.