At a news briefing, Boulder Police Chief Maris Herold told reporters her office along with 25 other law enforcement agencies were working around the clock to determine why the 21-year-old suspect chose Boulder, some 30 miles from his home in Arvada, Colorado, and why this grocery store.
Officer Eric Talley, who was one of 10 people killed during the shooting at King Soopers on March 22, was shot after he led his fellow officers and engaged with the gunman following calls that were made to 911.
Doughtery said the suspect was charged with attempted murder, along with the 10 murder charges because of his exchange of gunfire with officers at the scenes.
Officials revealed that Alissa also had another firearm in his possession at the time of the shooting that he did not use - a 9mm handgun.More news: Woman says Gov. Cuomo forcibly kissed her cheeks in 2017
"Like the rest of the community, we want to know why".
She said it would be "haunting for all of us" until they are able to establish why the shootings happened.
The police officer who was murdered during the recent grocery store shooting in Boulder, Colorado, was the last person killed, according to authorities.
Alissa purchased the Ruger AR-556 pistol, a weapon that resembles a semi-automatic rifle, after passing a background check.More news: Huge ship blocking Suez Canal partially refloated, more work needed
The suspect, being held without bail, has been transferred to another unspecified lockup outside Boulder County "due to safety concerns and threats that our jail staff became aware of", sheriff's spokeswoman Carrie Haverfield told Reuters.
Asked whether authorities suspected any link to worldwide terrorism, the DA said investigators were looking into all aspects of Alissa's background. "Ensuring every sale that occurs at our shop is lawful, has always been and will always remain the highest priority for our business", Eagleton wrote.
Colorado has enacted laws that require background checks for gun purchases, limit the ammunition magazine capacity and enable courts to temporarily seize the gun of someone deemed unsafe.
A lawyer for the accused requested a delay in further proceedings to allow for Alissa to have a mental health assessment.More news: Biden says Justice Department looking into Georgia election law