The Massachusetts Air National Guardsman accused of leaking classified U.S. documents used his government computer to research mass shootings, amassed an “arsenal” of weapons, and debated turning an SUV into an “assassination vehicle,” according to new court filings. Federal prosecutors say that Jack Teixeira, 21, had a previous history of violent and racial threats, and held “regular discussions about violence and murder” on the same online platform where he allegedly leaked the classified documents in one of the largest breaches of U.S.