BREAKING: Mass Shooting At Boulder Colorado SuperMarket, 10 Dead Including Police Officer (GRAPHIC VIDEO)

Ten people were killed, including a veteran police officer, during a mass shooting Monday inside a grocery store in Boulder, Colo., authorities said at a late press conference.

The officer was identified as Eric Talley, 51, who served on the force since 2010. He was the first officer at King Scoopers, the crime scene, after the shooting occurred at about 2:30 p.m. His actions were called heroic.

The suspect, who was not identified, is receiving medical treatment. Officers had escorted a shirtless man with blood running down his leg out of the store in handcuffs but authorities would not say if he was the suspect.

Identities of the other nine victims were not disclosed as police were still notifying their family members.

Authorities said that they are working to compile evidence. Several state and county law enforcement agencies were assisting Boulder police as well as the Bureau of Alcohol, Tobacco, Firearms and Explosives.

Witnesses told FOX 31 Denver that they heard pops that sounded similar to fireworks and saw a man brandishing an "AR-15 style weapon" and wearing what looked like tactical gear.

KCNC-TV reported that family members were in line for the COVID-19 vaccine inside the store's pharmacy at the time of the shooting.