Ahmad Al Aliwi Alissa, the primary suspect in the Boulder mass shootout case bought the Ruger AR-556 pistol gun legally from Eagles Nest Armory in Arvada city, officials said on Friday. 

He also had a handgun with him on the day of the shooting. 

Alissa is to be charged with 10 counts of murder and an attempted murder charge as per officials. A Boulder police officer also lost his life in the shootout. 

Also Read: Police use killed officer's handcuffs to take Boulder shootout suspect into custody

Boulder's Police Chief Maris Herold and County District Attorney Michael Dougherty said in a briefing that the motive behind Alissa open firing in the supermarket is still unknown. They are still trying to find out the motive, reported Reuters. 

Herold said, "Like the rest of the community, we want to know why. Why that King Soopers, why Boulder, why Monday, and unfortunately we don’t have those answers. It will be something haunting for all of us until we figure that out."

The shooter's brother said that Alissa suffers from paranoia. His lawyer asked for a complete mental health assessment on Thursday

Dougherty further said that the 21-year-old suspect may face additional attempted murder charges in the following weeks.

According to Doughtery the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) and the FBI are investigating the arms that the shooter had with him on the day he open-fired along with any other weapons Alissa's name is linked with. 

"If you picture a supermarket, picture all of the shelves, all of the products and everything. They are going through every single shelf," Dougherty added.

Also Read: Man detained in Atlanta for carrying multiple firearms in a supermarket

The owner of the store where Alissa bought the gun from said the shooter passed a background check before the purchase. 

"We are absolutely shocked by what happened and our hearts are broken for the victims and families that are left behind. Ensuring every sale that occurs at our shop is lawful has always been and will always remain the highest priority for our business," said John Mark Eagleton. 

The recent gun shootings have sparked mass outrage and debate about gun control in the United States. 

The gun control laws passed in Colorado limit the capacity of magazines to 10 rounds, enable courts to temporarily seize guns from someone considered dangerous and includes background checks before gun purchases.