Hatton Garden Safe Deposit

In April 2015, a heist at a London safe deposit facility, valued at up to £14 million, was carried out by six elderly thieves. While £4.3 million was recovered, the rest remains missing. The thieves were arrested, convicted, and sentenced in 2016.
#12 I lived in Boston from 1984 to 1994, The Gardner Museum was always my favorite of the many Boston area museums. I've must've visited it at least 40 times. I was actually there the day before the robbery with my then girlfriend. I've always considered myself lucky to be one of the last people to see those stolen works in person.