Parents who lost their children in the mass shooting at Sandy Hook Elementary School say they know all too well what the families of victims of the Orlando nightclub shooting are going through right now.

The Sandy Hook families say the Orlando tragedy, which took 49 lives and injured more than 50 others, takes them right back to December 2012 when they became a national story. Officials say the Orlando attack is the deadliest mass shooting in modern American history.

The Newtown Action Alliance held a vigil Sunday night to show its support to the Orlando victims.

Mark Barden and Nicole Hockley lost their sons in the mass shooting at Sandy Hook Elementary that killed 20 children and six adults.

Hockley says when she found out about the tragedy in Orlando, it brought her right back to the day her son Dylan was gunned down 3 1/2 years ago. 

She also says she can relate to the agonizing wait many families are going through in Orlando as the victims are slowly identified.

Barden says as police release information about the shooter, it's apparent there were warning signs.

His group, Sandy Hook Promise, is working to educate people to recognize the signs and speak out in an effort to prevent another tragedy.