Guns drawn, the officers rounded the corner of a Massapequa Park elementary school chasing a shooter on the loose.
As the cops made their way down a hallway, chaos erupted all around them. The principal came running toward them. Victims screamed for help.
Adrenaline pumping, there was no time to assist the wounded. The group had an "active shooter" to find.
It was all very realistic, but there was no real danger.
The scenario was carefully planned by Nassau County police as a training exercise last week for county residents at the department's civilian police academy. The man posing as the gunman: an officer wearing a dark sweatsuit and baseball cap.
But the exercise still had hearts pounding, participants said.
"It's harder than it looks beyond any measure," said David Sabatino, 28, a coffee shop owner from Valley Stream who played the role of an officer. "It's way more manic. It's chaos; it's emotional . . . eye-opening."
The civilian academy, which started in 1997 as a way to teach the public about policing practices, began holding classes in February -- seven years after it became a county budget casualty. The 15-week seminar, which covers topics such as gangs, drunken driving and the use of technology to fight crime, was last held in 2007.
The academy was revived when the nonprofit Nassau County Police Department Foundation decided to pick up the roughly $10,000 cost, which covers overtime pay for police instructors, said Alexandra Nigolian, the foundation's executive director.
"It's a great program," she said. "It really brings the department and the community together. The department relies on its relationship with the community in their efforts in public safety."
About 40 students, drawn from a pool of more than 70 applicants, were selected by police and community affairs officials, who consider civic involvement a prerequisite. The class meets Thursday nights at the Nassau police academy at the former Hawthorne Elementary School in Massapequa Park.
Suffolk police host a 16-week civilian academy, which began about 12 years ago, officials said.
Nassau police Sgt. Richard LeBrun, a police academy instructor who also heads the civilian program, said the latter strives to inform residents "why police do things certain ways."
"These people are our ambassadors now," LeBrun said of his students. "They can go back in the community and explain why we take certain tactics."
The "active shooter" training provided to a recent class mirrored the training that all Nassau officers get, said Sgt. Michael Savino, a 28-year veteran who runs the department's active shooter training.
Nassau and police departments across the country used to set up a perimeter and call in special units -- the Bureau of Special Operations and Emergency Service Unit -- to handle such incidents, Savino said. That changed after the 1999 massacre at Columbine High School, with officials realizing those long-held practices wasted precious response time.
Now, every Nassau and village police officer is trained to respond to an active shooter scenario, Savino said.
Savino described -- and later presented through role play -- how officers are trained to remain composed and search for the gunman even as victims are crying for help.
"We keep walking," he said. "We can't stop and help someone when a shooter's in the other room killing 10 people."
In the training exercise, students were armed with guns with firing pins removed.
Afterward, Michael Morelli, 18, a college student and Boy Scout from Wantagh, said the class has given him a new perspective on policing.
"Someone's shooting at you; it's very stressful," he said. "You think the officer could just take them out in two seconds. It's not that easy."