Boulder: A 21-year-old man faces 10 counts of murder in connection with a mass shooting at a Colorado supermarket, but his motive remains unclear, authorities say.

The suspect, identified by police as Ahmad Al Aliwi Alissa, was in a stable condition after he suffered a leg wound in an exchange of gunfire with responding police officers at the King Soopers outlet in Boulder, about 45 kilometres north-west of Denver, on Monday afternoon, local time.

The 10 victims, whose names were released at a Tuesday morning news conference, range in age from 20 to 65 and include Eric Talley, an 11-year veteran of the Boulder police force. Talley, 51, was the father of seven children and had recently been looking for a less dangerous job, according to a statement released by his father.

Police identified the nine other victims as Denny Stong, 20; Neven Stanisic, 23; Rikky Olds, 25; Tralona Bartkowiak, 49; Suzanne Fountain, 59; Teri Leiker, 51; Kevin Mahoney, 61; Lynn Murray, 62; and Jody Waters, 65.

Authorities have not yet offered a possible motive for the bloodshed, which came six days after a gunman went on a killing spree in the Atlanta area, fatally shooting eight people at three day spas before he was arrested.

“It would be premature for us to draw any conclusions at this time,” Michael Schneider, the agent in charge of the FBI’s field office in Denver, said at a news briefing about a possible motive for the killings.

The suspect lived in Arvada, a Denver suburb, and investigators said they were confident he had acted alone.

Monday’s attack, which began about 2.40pm, drew hundreds of police officers to the scene and sent terrified shoppers and employees fleeing for safety. The massacre added to the Rocky Mountain state’s tragic list of mass killings, including the 2012 mass shooting at a movie theatre in Aurora and the 1999 rampage at Columbine High School near Littleton.