BOULDER, Colo. — Investigators searching for answers after the mass shooting in Boulder, Colo., this week still do not know why a gunman shot and killed 10 people at a crowded grocery store, the police chief said on Friday.
“We, too, want to know why,” the Boulder police chief, Maris Herold, said at a news conference. “Why that King Soopers? Why Boulder? Why Monday? And unfortunately, at this time, we still don’t have those answers.”
The semiautomatic weapon used in the shooting was legally purchased six days earlier at a gun store in Arvada, Colo., the chief said. That weapon, a Ruger AR-556 pistol, is essentially a shortened version of an AR-15-style rifle and is considered a handgun under Colorado law.
The 21-year-old suspect, Ahmad Al Aliwi Alissa, was also found with a 9-millimeter handgun, but the authorities do not believe he fired it, the chief said.
Officials pledged to chase every lead and said they were working to determine whether there were any connections between the gunman and anyone in the supermarket. But they acknowledged the possibility that the gunman’s motives might never be known. It is not yet clear whether Mr. Alissa had ever been to the grocery store — which is about 15 miles north of his family’s house in Arvada — before the shooting, Chief Herold said.
“Sometimes you just don’t figure these things out, but I’m hoping we will,” she said.
Mr. Alissa has been charged with 10 counts of murder and one count of attempted murder and is being held in jail without bond. He was moved to a jail outside of Boulder County because of unidentified threats, a spokeswoman for the Boulder County Sheriff’s Office said on Friday.
At Mr. Alissa’s first court appearance on Thursday, one of his lawyers suggested that he had a “mental illness” but did not go into detail. Mr. Alissa, who was wounded in the leg before being taken into custody after a shootout with the police, appeared in court in a wheelchair.
Michael Dougherty, the Boulder County district attorney, said on Friday that he planned to file additional charges of attempted murder. He said the F.B.I. and the Bureau of Alcohol, Tobacco, Firearms and Explosives were looking into the weapons that the gunman was found with at the scene “and other firearms in his possession,” though he did not elaborate.
A manager of the gun shop where the AR-556 was purchased, John Mark Eagleton of Eagle’s Nest Armory, said in a statement that Mr. Alissa had passed a background check and the sale had been approved by the Colorado Bureau of Investigation.
“We are absolutely shocked by what happened, and our hearts are broken for the victims and families that are left behind,” Mr. Eagleton said. “Ensuring every sale that occurs at our shop is lawful has always been and will always remain the highest priority for our business.”
Mr. Dougherty said the grocery store was still being analyzed by investigators, a painstaking process that includes going through every shelf of food and other items in search of bullets or other evidence.
In response to a question, he said that the F.B.I. is still looking at any possibility of connections to international terrorism.
“At this point we don’t have any particular information to share in that regard,” he said. “We will continue to look into it.”
But those inquiries are part of a wide-ranging examination of any possible motive that still has produced no answers, he suggested.
“I think the victims’ families and the community are desperate to know the motive,” he said. “Whether or not we’re able to determine it remains to be seen.”
Among the victims were at least three employees of the store, King Soopers, and Officer Eric Talley, the Boulder police officer who was the first to respond to the scene.
An officer who fired his gun at Mr. Alissa has been placed on administrative leave, a standard move after a police shooting, the authorities said.
Jack Healy reported from Boulder and Nicholas Bogel-Burroughs from New York. Ali Watkins contributed reporting from Boulder.