Sunday is the second anniversary of the shootings that claimed the lives of 20 children and six educators at Sandy Hook Elementary School. One of the groups formed in the aftermath of that tragedy, Sandy Hook Promise, has released a powerful video that tells the story of three families who lost children to gun violence. One thing the three stories have in common is missed opportunities.

One is the story of a 16-year-old boy killed by a friend fooling around with his father’s shotgun, which had been left in an unlocked closet. The victim’s best friend said of the evening that ended in his death: “There were so many red flags that night and we just ignored them. We were kids that thought this would never happen to us.”

The second story was about a depressed teenager who killed herself with a gun she took from the trunk of her policeman father’s car. While she deflected concern from her family, she posted extensive notes on social media platforms about her suicidal feelings. They’re painful to see, including a tweet: “It’s like God is torturing me keeping me here.”

The third story is that of a 7-year-old boy killed at Sandy Hook. His father, thinking of the shooter, talks of the tragic combination of isolation and access to guns. But he also says, “This doesn’t happen overnight or in a week. There had to be multiple markers, multiple opportunities to intervene” that might have prevented the tragedy.

Here’s the note he closes on, and a message we endorse: “I think our responsibility as parents transcends our own children; we also need to look out for our neighbors and their children.” He notes that sometimes an outsider “will notice and bring light to something almost too close for a family to see.”