The building that houses The Mob Museum began its life as the first federal structure in Las Vegas. It held the city’s main post office, federal courtroom and offices for various federal agencies. This new documentary, “This Building of Ours,” details the federal building’s central role in Las Vegas life during the 20th century and its reinvention as The Mob Museum in the 21st century. For decades, the post office on the first floor was a bustling community gathering place, while the courtroom on the second floor played host to a number of highprofile trials and hearings, including the Kefauver Committee hearing on organized crime in 1950.