Sandy Hook Victim's Father Pens Open Letter to Dad of Student Killed in Santa Barbara Massacre

By Carlos Greer

05/28/2014 at 06:40 PM EDT

Mark Barden and Richard Martinez

Michelle McLoughlin/Reuters/Landov; Lucy Nicholson/Reuters/Landov

As families try to make sense of the deaths of their children from a man who went on a shooting and stabbing rampage in Santa Barbara, one Sandy Hook father wants them to know they are not alone.

Mark Barden, who lost his 7-year-old son, Daniel, in the 2012 Sandy Hook school shooting, penned a letter to Richard Martinez.

"We have not met, but you are now part of our extended family," writes Barden. "It is not a family we chose, but a family born from the horrible circumstance of losing a child to gun violence – one that's growing steadily."

Barden posted his letter to Martinez from the non-profit Sandy Hook Promise's group page on Facebook.

"My heart breaks for you because I know just a little about the long road ahead of you. We have reached out to you privately but publicly we wanted to say to you and those feeling the sorrow, anger and frustration of this weeks' shooting, you are not alone," he wrote.

Martinez, whose son Chris was one of seven who died, has been speaking out about gun violence since the tragic accident.