WASHINGTON -- Priorities USA, a super PAC supporting Democratic presidential candidate Hillary Clinton, released a powerful digital ad Friday that features Peter Read, whose daughter Mary Read was killed during the massacre at Virginia Tech in 2007.

Read, a retired Air Force lieutenant colonel, recalls seeing news of the shooting on television and trying to get ahold of his 19-year-old daughter. She was one of 32 students and faculty killed that day, in what remains the nations deadliest shooting rampage by a single gunman.

Hillary Clinton is addressing the issue of gun violence prevention, Read says in the ad. Its clear from the way she talks about it that shes talking from conviction, and I do think Hillary Clinton has been very forthright in calling out the leadership of these organizations like the NRA.

I wish we never had to talk about it, but we have to talk about it, and she is, he adds.

The web spot, called Conviction, was first shared with The Huffington Post. It is the third in a series released by the super PAC, which spent six figures on ads ahead of the Iowa caucus Monday. The other spots in the series were 30 seconds long and each highlights multiple issues, from Clintons stance on Wall Street reform to Planned Parenthood funding, so this third spot is unique in that it's 60 seconds and focuses on a single issue.

Clintons campaign and her allies have worked to draw contrasts between her record on gun safety and that of her main competitor for the nomination, Sen. Bernie Sanders (I-Vt.). While Sanders has repeatedly said that he has a D- rating from the NRA and supports banning assault weapons and instituting universal background checks, Clinton has highlighted his vote in 2005 to shield gun makers and dealers from legal liability, and a vote against the Brady bill in 1993 that created the federal background checks system. Clinton frequently criticizes the NRA for its advocacy against gun control of any kind as she campaigns, and has called for a national movement to convince lawmakers that more should be done.

Read was at the White House earlier this month alongside President Barack Obama as he announced new steps his administration would take to strengthen background checks and devote additional funding to mental health services.

Peter Read is one of too many parents who have suffered in a way that no one ever should, said Guy Cecil, Priorities USAs chief strategist. We need leaders like Hillary Clinton who arent afraid to stand strong against powerful special interests like the NRA and politicians who do their bidding in the face of these senseless acts of violence.

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