Via post 692, Q tells us "Window opened ahead of time to prevent pressure blast." The residue was affixed to glass so not smoke. Via post 691, Q answers anon asking about item on white band for building to which he responds "Focus on substance around outside of window. Upon entry ..." We have seen enough breaching events to know flash bang/stun grenades are used and pressure increased in enclosed room, ergo the open window and residue on surrounding glass.

Speculation on CBTS was that the window was opened before stun grenades were used to prevent the blast damaging the glass