Dec. 15, 2012 -- Police and paramedics who descended on the scene of the massacre at a Connecticut grade school face haunting memories and nightmares in the days and weeks to come, particularly if they have children of their own, experts say.
Twenty children and seven adults were killed Friday after a gunman opened fire at Sandy Hook Elementary School in Newtown, Conn. The shooter, identified as 20-year-old Adam Lanza, then killed himself.
"How the first responders react depends on how closely they identify with the victims," said Dr. Charles Marmar, chair of psychiatry at NYU Langone Medical Center in New York City. "Let's say somebody has a son or a daughter the same age as the victims -- we know that makes a big difference."
After the initial shock of such a violent attack fades, first responders sometimes struggle with flashbacks and sleep disturbances that can take a personal and professional toll.
Neal Schwieterman, a first responder at the 1999 Columbine massacre, still struggles with memories of what he saw there.
"Part of me is still missing from that day," said Schwieterman, who was a sheriff's deputy in his last week with the Jefferson County Police Department at the time. "I will never be the same."
Schwieterman rushed to the scene where he evacuated eight carloads of wounded students.
"It's a grieving process for everyone after this kind of thing, including first responders," said Schwieterman, who sought counseling to cope with the harrowing day. "It took a complete toll on me, and rightfully so."
Schwieterman was not a father at the time, but now has a 10-year-old daughter.
"I just can't imagine," he said of the Newtown shooting. "It rips your heart out."
Experts say first responders are surprisingly resilient, with the vast majority recovering from the stress of a horrific scene within days or weeks.
"But some will continue to have symptoms, and those people will probably benefit from some form of counseling," said Dr. Spencer Eth, a professor of clinical psychiatry at the University of Miami. "Unfortunately, when it comes to police, they sometimes try to act tough even when they're feeling badly, and that's an obstacle to getting the help they need to recover."
The fact that most of the victims in Newtown were children, Eth said, could mean more first responders will need counseling.
"The shock and horror of seeing children killed is more personally distressing than almost any other situation they have to deal with," he said, adding that first responders in many cases are also responsible for notifying families of the deceased. "Having to notify parents of their child's death is among the most difficult things they have to do in their professional lives."
With help, first responders can learn to cope. But they can never forget. Schwieterman, who is now the mayor of Paonia, Colo., still speaks of Columbine with a shaky voice, pausing often to gather himself. And when he heard about the Newtown shooting, he knew his phone would be ringing.
"I've had several family members call and ask if I'm doing OK," he said. "That kind of support helps you through these things."