Where there’s smoke, there’s fire.
The smoke was a clever screen, there was no fire but no one knew that. The gas canisters did exactly what they said on the tin and masked the whole area in a think stinking fog that billowed seemingly out of control. Panic set in. Exits were stormed and people were trampled underfoot in the frenzy to preserve life. Emergency sirens, deafened by the screaming did little to calm the situation. Help was on hand but no one took any noticed. Jewels were stashed in the backpacks, and the heist instigators joined the melee of people ushered to safety, undetected.