SAN FRANCISCO - When a California college student was shot dead by a stranger on a crowded commuter train in San Francisco last month, none of the dozens of passengers on board saw it coming - they were too absorbed in their mobile devices, officials said on Wednesday.
Surveillance footage of the incident last month showed a train car full of passengers within feet of the accused gunman as he openly brandished a weapon on the train, they said.
Nikhom Thephakaysone, 30, is accused of firing a single fatal shot at San Francisco State University student Justin Valdez "for no apparent reason" as the 20-year-old college sophomore was getting off the train near the university, San Francisco police Chief Greg Suhr said.
San Francisco District Attorney George Gascon said surveillance video showed people on the train texting and talking on the phone at the time of the Sept 23 incident, not noticing a man brandishing a gun close by.
He said the killing highlighted concerns that people on smartphones or other mobile devices might be at risk of missing signs of impending dangers.
"As our society integrates technology like smartphones into our daily lives, it has become evident that the distractions created by these devices can lead to dire consequences," he said.
"I'm hopeful that consumer behaviour will change, and that people will consider the risks posed when they lose track of their surroundings," Gascon said. "After all, a life can be ruined in the blink of an eye."
The gunman got off the train and walked home after the shooting.
Police say he pointed his gun at strangers in at least two other incidents on the night of the shooting before being arrested at his family's San Francisco home the next day.
Police said they found three firearms there, US$20,000 (S$24,900) in cash and a backpack full of survival gear, including combat knives, razors, a flashlight and a first-aid kit. Police did not immediately know why he may have had the paraphernalia.