placing a container with a powdered nerve agent into the air vent
Wait, then enter with full masks and gear, go into the vault area, drill thru the top, fill the vault with water, drop a timed high-explosive inside of it.
detonate, and remove whatever boxes of jewerly/ect you want. and set off a high-explosive in a random office building across town. That should distract most of the PD.
The ones left can be taken out. Corner snipers on the upper buildings. Armed with sako Trg-42's. .338 lapua magnum rounds, preferrably custom hand-turned armor peircing.
at which point move loot to a small lake, and use a sea-plane to fly to a miami harbor. Boat to the cayman islands and then devide profits/win.
Also, as a police deterant, place fake fire-hydrants conceiling high-explosives wrapped in ball bearings with remote detonators along the street. What officers do show up get the pleasent suprise of dealing with psuedo-claymores.