It begs the questions 'could this have been prevented?' and 'are there enough resources to help people with mental illness?'
Dr. Anthony Rostain, Professor of Psychiatry and Pediatrics at Penn Medicine, says while great strides have been made in understanding the science behind mental illness, there is still a huge gap in getting people help.
One reason is insurance coverage.
"Most people even with good health insurance often don't have the coverage they need if they have serious mental illness," Rostain said.
Plus, he says the system is in disarray.
"It's underfunded; it's being cut as we speak," Rostain said. "So I am very worried, I think while the incidence of mental illness is going up, I don't think we are keeping up with resources we need to get the job done."
Also a huge barrier is that some with mental illness don't want help.
"They're paranoid, they're afraid of what's going to happen," Rostain said.
And in most states, anyone 18 or older can't be forced into treatment; they have to consent.
Most serious mental health problems such as schizophrenia tend to peak in early adulthood.
We don't know what happened with Adam Lanza, but he and past gunmen such as the man accused in the Aurora movie theater shooting or the man who injured Congresswoman Gabby Giffords and killed 6 others in Arizona were between 20 and 25 years old.
Still Dr. Rostain cautions not everyone with serious mental illness is violent.
In fact, he says most are not, but all do need help and we as a nation need a better way to recognize and treat mental illness early.
Dr. Rostain says raising awareness is a start. Plus, he'd like to see screening for more mental health problems done at routine medical appointments.