Washington DC has numerous police departments. MPDC is the city police department. The US Capitol has the Capitol Police Department. The US Park Police is a part of the Dept of Interior and they have a sizeable police department that includes the only helicopters in the District. There are many other police departments, including the Sup Court, National Zoological Police, US Secret Service Uniformed Division, FBI Police Department, Amtrak Police, Federal Protective Service, etc...

The first MPDC units to arrive were met by the Capitol Police Emergency Response Team (ERT). MPDC asked the Capitol ERT for assistance and the Capitol Police on duty Watch Commander ordered his ERT to stand down. There are no guarantees that ERT would have made any difference, but then again, earlier response may have made a difference. There is just no way of knowing what would have happened after the fact.

DC is a strange place to work.