THERE is an unspoken rule in medicine: we do not tell tales out of school.

As an emergency room physician, an Army veteran who was deployed to a combat support hospital in Baghdad in 2005, and a biomedical researcher in the field of cardiac-arrest resuscitation, I have been and am, on a daily basis, a witness to grave misfortune. Ordinarily, though, except for medical purposes, I will not discuss what I have seen.

Last week a colleague asked me to make an exception. The father of two young children, he was moved by the rampage at Sandy Hook Elementary School in Newtown, Conn., to ask his professional circle to reconsider our silence. I am an expectant father, and his words resonated with me. They reminded me that we doctors are at the front lines of the scourge of gun violence, and that to remain silent as this threat to public health continues unabated would be no different than for an oncologist or a cardiologist to stay mum on the dangers of smoking.

The doctor’s balance between discretion and education is complex. But the news from Newtown, and my colleague’s request, convinced me that we have reached the threshold. I can no longer stay silent.

Here is just some of what I have seen over the years. In Baghdad, I saw a 5-year-old girl who was shot in the head while in her car seat. Her father, who knew she was dying before I said it, wept in my arms, as bits of her body clung to his shirt.