“Major Investigation Department! I got a Section 3A!”
-- Tina Goldstein (WFT)
Part of the Magical Congress of the United States of America (MACUSA), the Major Investigation Department appears as a meeting room in which high-up MACUSA employees discuss ongoing investigations.
The MACUSA Aurors, along with President Picquery, meet in the Major Investigation Department to discuss the strange goings on around New York in December of 1926. Percival Graves (really Grindelwald) is present at the meeting.
The Major Investigation Department is first referenced when Tina takes Newt Scamander to MACUSA headquarters to report him.
The room also holds a metallic map of New York City that lights up to show areas of intense magical activity.