"People need to be cautious," Bloom says.

But depending where someone is in his or her recovery, there can be another response to a tragedy, Bloom says. Survivors may feel a sense of strength to help shattered families because of their ability to empathize.

"You can be inoculated, welled up with compassion and less of the fear because you know you can get through to the other end, because you've been there. People who have been through this have found a way to create meaning," she says. "People take their experience and transform their pain into power. It's psychological alchemy."

That's something Columbine survivors are working to achieve. Their thoughts and prayers are with the families in Connecticut.

"It's taken me years to get to the point where I'm at now," says Graves. "It's been a struggle, and it's been painful and emotional. But to see a bunch of families have to go through this -- they're just starting their journey now. I wouldn't wish this on my worst enemy."

Wheeler and some other survivors and their parents have created a group called The Rebels Project to reach out and help survivors of mass shootings and families of victims.

"We have parents who had to carry us through dark ages and try to get us to be normal citizens," she says. "These parents know how to speak to parents. They are working to do something for Connecticut."

The project was started this past summer, after a gunman opened fire at a movie theater in Aurora, Colorado, killing 12 people.

Some people in the Aurora community who were traumatized by that mass killing have already been calling a hotline in the city, says Mara Kailin, program director at the Aurora Mental Health Center.

"We've been hearing from from first responders and folks in the community that were directly impacted," she says. "They're wanting to help people in Connecticut -- and being reminded of what we went through a very short time ago."