Gadget-Absorbed Commuters Failed to Notice Gun Before Fatal Shooting

Oct. 10, 2013— -- Gadget-absorbed passengers on a San Francisco train were too distracted to notice a gunman brandish his firearm before he allegedly shot a 20-year-old man to death, the district attorney said.

Justin Valdez of Garden Grove, Calif., was allegedly shot in the back of the head as he exited a train last month by a man who flashed his .45-caliber pistol several times on the train, authorities said.

Officials came to that conclusion after they reviewed Sept. 23 footage from a surveillance camera on the San Francisco Municipal Railway car. Authorities have not released the surveillance video to the public.

Suspect Nikhom Thephakaysone, 30, has pleaded not guilty to charges including murder and assault with a semi-automatic handgun. He is expected to appear in court Nov. 20. Thephakaysone is being held without bail.

The footage, according to San Francisco District Attorney George Gascon, shows Thephakaysone brandishing the gun "at least three or four times" and at one point he raised the gun near his face.

"You can see people sitting or standing around him and they are busy working with their tablets or their mobile smartphones, completely distracted," Gascon told ABC News.

Valdez was standing across from Thephakaysone with his back toward him and didn't appear to notice the gun either, according to Gascon.

"We're not seeing the entire car but there were easily eight to twelve people right in that immediate area within probably two to three feet away from him at the time," Gascon added. "It's very disturbing because the lack of awareness of your surrounding is so blatant in this case."

Thephakaysone stepped out of the train slowly when the train came to a stop and allegedly fired one shot to the back of Valdez's head, Gascon said.

"[Thephakaysone] ran away and people started reacting but, unfortunately, prior to that people were completely distracted and not seeing what was occurring," he said.

Police say the two men didn't know each other and the shooting was unprovoked.

"My brother was completely innocent and there was no reason for him to be killed. He was too young to die," Valdez's sister, Jessica Labidi, told ABC News."I always try to stay strong and I know that God has a reason even though it seems completely random and unexpected."

Officials arrested Thephakaysone four hours later at his home where they allegedly confiscated assault rifles, $20,000 in cash, ammunition and "some survivalist type clothing and equipment," Gascon said.