About 1:15 a.m., the teen was video-chatting — police believe it was either over Skype or another video-chat service called ooVoo — with an as-yet-unidentified person while his brothers were asleep in the room in their Kensington house.
Sometime during the video chat, things went horribly wrong.
"His manhood or his ego was challenged and he said something along the lines of, ‘I'll show you,'" Gallagher said. "He thought he was clowning around, trying to shock the other party on the Internet site."
That's when the teen picked up his older brother's gun and, believing it was unloaded, put it to his head and pulled the trigger, police said.
Outside the house Wednesday morning, the mother of the boys sat sobbing as her sons waited in the back of police cruisers to be taken in for questioning.
A neighbor on the block, Cumberland Street near Jasper, was nearly speechless.
"Oh, my God, it's so sad. It's so sad. I'm sick to my stomach," the woman said, before rushing down the block to comfort the distraught mother and offer her a sweater on the unseasonably chilly night.
Police said the older brother — listed in news reports as 22 years old — had purchased the firearm about a month ago and still had the box for it inside his room. He told police he, too, believed the gun was unloaded.
Gallagher said the gun was bought at a local store and investigators were heading there to verify whether it was purchased legally.
Police also were trying to determine who was on the other end of the chat when the shooting occurred. They'd like to interview that individual and find out if video was captured.
Although the investigation continues, Gallagher said, the shooting appears to have been accidental.
"It looks like there's no indication of a suicide attempt, a depressed individual or a struggle," he said.
Gallagher said everyone should treat every gun as if it were loaded and those who purchase firearms should first have to pass a safety training course, something that is not required now under state law.
"I've seen more people under these types of circumstances killed by an ‘unloaded' weapon like this," he said. "My heart bleeds for the family. I'm sure everybody in that household wishes they could take that bullet back."
— Staff writer Morgan Zalot contributed to this report. Reach Stephanie Farr at firstname.lastname@example.org or 215-854-4225. You can also follow her on Twitter @FarFarrAway and read her blog "Philly Confidential" at PhillyConfidential.com