A large scale drill involving state and federal first responders took place Tuesday through Thursday about what to do in a terrorist attack scenario involving transit commuters.  Investigators combed through the site of a Metro North train car on its side with mannequins around. 

Public Health Preparedness and Response Director John Best says the most important aspect of the drill is how agencies work together.  Best says no one ever expects a mass casualty event in a small town, but that's exactly what they learned from the aftermath of the shooting at Sandy Hook School. 

The last mass fatality event in Connecticut was 12/14/12.