A law enforcement officer was among ten people fatally shot in a domestic terrorist attack at Soopers supermarket in Boulder, Colorado on Monday.

The suspect, whose identity has not been released, was taken into custody and is being treated for injuries, officials said.

The slain officer, 51-year-old Eric Talley, had been with force since 2010 and was responding to the incident when he was killed.

Michael Dougherty, district attorney for Boulder County, gave an assurance that officials at every level will be involved in the investigation as well as prosecutors from the US Attorney’s Office.

The investigation is expected to take at least five days, according to Boulder Police Chief Maris Herold.

“My heart goes out to the victims of this incident, and I’m grateful for the police officers that responded and I am so sorry about the loss of officer Talley, and again we will be here working night and day,” she said.