LOS ANGELES (Reuters) – Three weeks after a former U.S. Marine opened fire at a Western-themed bar and dance hall in the Los Angeles suburb of Thousand Oaks, killing 12 people, police said on Tuesday they still had no clue what prompted the massacre.

Ventura County Sheriff Bill Ayub said the gunman, who took his own life as police closed in at the shooting at the Borderline Bar and Grill on Nov. 7, did not appear to have been radicalized and left behind no written manifesto.

“As to the motive of the suspect we are no closer to determining that today than we were at the onset of the incident,” Ayub told a news conference to update the progress of the investigation.

Law enforcement officials have said that 28-year-old Ian David Long acted alone when he stepped inside the bar filled with line-dancing college students and immediately began shooting, seemingly at random, with a .45 caliber Glock handgun.

Among those killed was Sergeant Ron Helus of the Ventura County Sheriff’s Office, one of the first two police officers to arrive at the bar. Helus was gunned down by Long from a position he had taken at the rear of the bar.

FORMER MARINE

Long served in the U.S. Marines from 2008 to 2013, reaching the rank of corporal and serving as a machine gunner in Afghanistan.

Ayub, who took over the county’s top law enforcement job days after the shooting, said Long purchased the Glock handgun legally at a gun shop in nearby Simi Valley, but was carrying seven high-capacity ammunition magazines that are banned under California law.

The sheriff said investigators were trying to determine how Long obtained those magazines, “although they can easily be purchased in another state.” He said that five remained loaded at the time of Long’s death.

Long also threw several smoke bombs in the bar, adding to the chaos, and stabbed one of his victims in the neck with a folding knife. A flashlight laser sight was attached to his gun.

At least eight off-duty law enforcement officers were inside the bar at the time of the shooting, but none returned fire at Long, Ayub said.

All 12 victims died almost immediately from their wounds, Ventura County Medical Examiner Dr. Christopher Young said, adding that none were struck by bullets from law enforcement.