We may never know exactly what was happening with the shooter, but many believe he was mentally ill.
Experts in the field say since this tragedy and others has brought more awareness in the community about mental health, and is helping people in need find treatment.
Dr. Arthur Evans is commissioner for the Department of Behavioral Health in Philadelphia. He says what happened in Newtown a year ago shined the spotlight on the importance of mental health services, and the current gaps in care.
"So one of the things we need to think about are people who need help who are not yet diagnosed," said Dr. Evans.
He says most of the mentally ill are not violent, but we now know we can't wait for someone to seek care for themselves.
Dr. Evans says Philadelphia tries to take a more proactive approach by going out into communities.
The city also had one of the largest rollouts of 'Mental Health First Aid' in 2012. It teaches everyday citizens how to handle mental illness.
"The best way to describe it, it is analogous to CPR," said Dr. Evans.
Meaning if someone has a heart attack, many in the community know what to do. But when someone is having psychiatric problems, most people don't know what to do.
"What mental health first aid does is gives people the skills and knowledge to act when a person is showing signs and symptoms of mental illness," Dr. Evans explains.
Since the tragedy at Sandy Hook, he says more people - teachers, first responders and businessmen and women- have signed up for the training.
"I think a year ago, I don't know that we would have gotten the response that we are getting today," he said.
The goal is to have 10,000 people in Philadelphia trained in Mental Health First Aid over the next few years. So far, they are about a quarter of the way there.
It is open to everyone in the city.
Dr. Evans believes the new healthcare law will also help more people get access to mental health services.
