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WATCH: Senate holds hearing on proposals to reduce gun violence

At the opening of a Senate Judiciary Committee hearing on gun violence, Chairman Sen. Dick Durbin said gun violence was a “public health crisis.”  Durbin added, he could ask for a moment of silence, but “in addition, I would like to ask for a moment of action. A moment of real caring.”

Watch the hearing in the video player above.

Police on Tuesday identified a 21-year-old man as the suspect who opened fire inside a crowded Colorado supermarket in an attack that killed 10 people, including an officer, and sent terrorized shoppers and employees scrambling for cover.

Investigators have not established a motive, but authorities believe he was the only shooter, Boulder County District Attorney Michael Dougherty said.

A law enforcement official briefed on the shooting told The Associated Press that the gunman used an AR-15 rifle, a lightweight semi-automatic rifle.

Hundreds of police officers from throughout the Denver area responded to the attack, converging on a King Soopers supermarket in a busy shopping plaza in southern Boulder.

In his opening remarks, Sen. Chuck Grassley, R-Iowa, acknowledged the response of law enforcement at the latest shootings while emphasizing the right to bear arms for America’s citizens. “In the dialogue about gun control, we rarely consider how many Americans are united in their advocacy and enjoyment of this right.”

This is the first of a series of hearings to examine proposals to reduce gun violence, focusing on public health, law enforcement, and community-based approaches aimed at making Americans safer. It was scheduled before the fatal shooting in Colorado.

One witness before the committee, Robin Brule, an advocate who lost her mother to gun violence sympathized with those who lost loved one in the recent shootings saying “Last week, my heart ached for those suffering from the tragic shootings in Atlanta. Last night, my heart ached for those suffering from the heartbreaking shooting in Boulder.”