A gunman has killed 10 people, including a police officer, following an hours-long stand-off at a grocery market in the US state of Colorado. The attack in Boulder ended with police detaining an injured suspect at the King Soopers market. The shooting was live-streamed by witnesses and broadcast on YouTube. Among the dead was 51-year-old Eric Talley, who was the first police officer to respond to the shooting. “This is a tragedy and a nightmare for Boulder County,” the area’s district attorney, Michael Dougherty, said.