The Brief A hazmat investigation is underway after an unknown white substance inside a sealed bag was discovered in a mail room near Mayor Karen Bass' office at LA City Hall. LAPD and fire officials are investigating the suspicious envelope, and City Hall has been temporarily closed to the public. Authorities said a hazmat situation is underway at City Hall in downtown Los Angeles after an unknown white substance was found inside the mail room near Mayor Karen Bass' office. What they're saying:"A suspicious envelope containing an unknown substance was found in a mail room near the Mayor’s office. City Hall is closed to the public for the time being," Mayor Bass' said in a statement.