Officials say the killing highlighted concerns that people on smartphones might not notice impending dangers. Justin Sullivan/Getty Images

Surveillance footage of the fatal shooting last month of a college student on a crowded San Francisco commuter train showed dozens of passengers too absorbed in their phones to notice the accused gunman as he openly brandished a weapon, officials said.

Recently released footage from a Muni security camera shows the alleged shooter as he pulled out a .45-caliber pistol, brandished it openly, pointed it across the aisle and continued to pull it out multiple times – even wiping his nose with the gun.

Nikhom Thephakaysone, 30, is accused of shooting and killing San Francisco State University student Justin Valdez "for no apparent reason" as the 20-year-old sophomore was getting off the train near the campus, San Francisco Police Chief Greg Suhr said.

San Francisco District Attorney George Gascon said surveillance video showed people within feet of the accused shooter texting and talking on their phones at the time of the Sept. 23 incident, not noticing the man brandishing a gun close by.

Gascon said the killing highlighted concerns that people on smartphones or other mobile devices may be unaware of impending dangers.

The alleged gunman got off the train and walked home after the shooting.

"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," Gascon said.

Police say the accused 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.

Wire services