bank of america
My favorite heist took place in the early '90s but I don't remember all the details.
What I do remember though is that two guys posed as cops and asked to enter a museum because of a disturbance complaint and the gullible security guards let them in.
As soon as they're inside the fake cops forced the guards down to the basement at gun point and tied them up.
Then they proceed to rob the place of a lot of valuables paintings just by cutting them off their frame.
The results: millions of dollars in stolen art (I guess they already had buyers aligned or they knew a good fence).