Ten people, including a police officer, were shot and killed at a Boulder, Colorado, supermarket on Monday, the second mass shooting in the U.S. in a week. 

At a news conference late Monday, authorities said the assailant was wounded and in custody, receiving hospital treatment. Citing the ongoing investigation, authorities didn’t reveal his name or any details about the shooting.

“This is a tragedy and a nightmare for Boulder County,” Boulder County District Attorney Michael Dougherty said. “These were people going about their day, doing their shopping. I promise the victims and the people of the state of Colorado that we will secure justice.”

The carnage occurred around 2:30 p.m. at King Soopers in Boulder, which is about 25 miles northwest of Denver and home to the University of Colorado.