By Jim Williams

NORTHBROOK, Ill. (CBS) — Police and fire departments in every community today have to prepare for the worst: mass shootings, terrorism. In Northbrook, we saw a new strategy for officers and paramedics. CBS 2’s Jim Williams was there

Three case studies: terrorism in Mumbai, India, the mass shooting at the movie theater in Colorado and the Boston Marathon bombing are all shaping a homeland security exercise in Northbrook.

“We learned we need to train together so we’re choreographed in that response and we can do it more efficiently and better,” said Tim Cassidy of the Northbrook Fire Department.

Multiple communities today learned what Winnetka Police Chief Pat Kreis calls a new model for emergency response.

In the old model, Kreis says, “Often times before this training we would focus on the police officers moving each patient out to a location to then transfer to the paramedics.”

Now, the police officers and paramedics are trained to go in together, officers securing the building while paramedics in bullet proof gear begin treatment right there, even in a gunfight.

“Law-enforcement needs to stop the threat,” Cassidy said. “We need to stop bleeding.”

The American Medical Association reports people at the 2013 Boston Marathon are alive today because they were first treated at the scene.

“The Boston Marathon bombing was a great example of how many lives are saved because of how quickly those wounded persons were moved into the EMS system,” Kreis said.

Before they saw a hospital emergency room.

Officials asked us not to disclose the identity of the building used in today’s homeland security exercise. We wanted to know if they’ve learned anything from the Paris attacks that might be useful in their drills. They told us it’s too early to determine.