CREDIT: Lilla Frerichs

Footage from a murder scene has San Francisco officials concerned that smartphones are a dangerous distraction. The San Francisco Department told the press that the security footage of the alleged killer of a man aboard the light-rail train had his gun in plain sight.

What investigators found alarming, according to sources, is that passengers of the train did not notice the killer because they were busy with their handheld devices.

A Municipal Transportation Agency security camera footage reveals that on September 23, a man named Nikkhom Thephakayson took out a .45-caliber pistol and raised it right in front of oblivious passengers. The video also shows Thephakayson pointing the gun across the train's aisle without anyone noticing.

Investigators say none of the passengers reacted until Thephakayson fired the gun at 20-year-old Justin Valdez, a student at the San Francisco State University.

The shooting was random, according to investigators. Authorities later found weapons inside the shooter's home.

George Gascon from the District Attorney's office told the Chronicle that the people inside the train were "so engrossed, texting and reading and whatnot." Gascon added that the passengers were "oblivious of their surroundings."

According to a 2009 study done by Ira Hyman of Western Washington University, when he had a clown ride a unicycle across the university, only very few people noticed him. Hyman also noted that those who were engrossed with their handheld devices did not notice the clown at all.

Smartphones: Threat to Personal Security

With the prevalent use of handheld devices and everyone looking at their cell phone screens wherever they go, it is easy to get in trouble. Literally bumping on people while in public areas may be one of the most common things that can happen to a person busy with his or her smartphone but more dangerous things can happen, experts say.

Walking with headphones on or while looking at your smartphone is not a smart idea because someone just might be following you. Listening to music, for example, gets rid of your capability to hear what is going on around you.

The San Francisco murder is one example to keep your cell phone in your pocket or purse while in public places.