Boulder Shooting: Gunman's Motive Still Unknown; Complex Investigation Underway

BOULDER, Colo. (CBS4) -- The Boulder Police Department held a news conference Friday morning on the ongoing investigation into the mass shooting at the King Soopers store on Monday. Investigators said the gun used in the shooting was purchased legally -- and warned it would take about a year before the case will go to trial.

Ten people, including one police officer, were killed at the King Soopers store at Table Mesa Drive and South Broadway. The suspect, Ahmad Al Aliwi Alissa, was taken into custody by police shortly after the killings.

Boulder Police Chief Maris Herold said the officer who shot the suspect has been put on administrative leave, which is standard operating procedures. That officer, an 11-year veteran of the police department, was not injured.

The firearm used by the suspect is a semi automatic Ruger AR-556 pistol. It was legally purchased at the Eagle's Nest gun store in Arvada.

The store released the following statement:

"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.  Regarding the firearm in question, a background check of the purchaser was conducted as required by Colorado law and approval for the sale was provided by the Colorado Bureau of Investigation.  We have and will continue to fully cooperate with law enforcement as their investigation continues."

The defendant was also in possession of a nine millimeter handgun, but investigators do not believe that gun was used in the store.

On Wednesday, the crime scene personnel finished the King Soopers lot parking, and many of the vehicles were released to owners.

"Yesterday, a team of investigators, including myself, did a walkthrough of the entire crime scene, which was very complex, and obviously very challenging to not only myself, but the investigative team," Herold said.

Investigators are going through the entire store, item by item, taking everything off the shelves to search for gunshots.

In the past five days, 167 people from 26 local, state and federal agencies have spent more than 3,000 hours investigating the shooting.

Herold and Boulder County District Attorney Michael Dougherty warned that it will take about a year before the case will go to trial.

Investigators still don't know why the gunman chose that store on that day.