Armed assailant waves gun but train passengers using phones and tablets don't even notice

An armed man waving a loaded .45-caliber pistol on a packed commuter train went unnoticed by passengers who were too busy looking at their phones and tablet computers.

Security footage allegedly shows Nikhom Thephakaysone, 30, waving a gun and pointing it across the aisle several times on the San Francisco-based train on Monday, each time failing to the draw the attention of any passengers.

Thephakaysone allegedly then opened fire on a random passenger, killing 20-year-old college student Justin Valdez.

"These weren't concealed movements — the gun is very clear," District Attorney George Gascon told the San Francisco Chronicle. "These people are in very close proximity with him, and nobody sees this. They're just so engrossed, texting and reading and whatnot. They're completely oblivious of their surroundings."

Thephakaysone plead not guilty to murder charges but police say that in addition to the train footage, they have video of him brandishing the weapon at another location prior to boarding the train. Authorities say they believe he was "hunting” for a potential victim when he boarded the train and was found carrying $20,000 in cash when he was apprehended.

Of course, smartphones and other portable electronic devices can be instrumental in solving crimes by revealing evidence that might otherwise go unnoticed .

For example, there has been plenty of criticism in the aftermath of the Boston bombings after users on social media sites posted inaccurate information. However, other experts have said the abundance of security footage and amateur video provided by witnesses was critical in the investigation.

Police say that as strange as it may sound, the fact that apparently none of the passengers noticed the gunmen before the shots were fired reflects a growing trend.

"Oftentimes when you interview people who get their phones stolen, when you ask them to describe where the person came from, what he was wearing, they have no idea," police Chief Greg Suhr told the Chronicle.