He flashed gang signs in selfies, posted a photo of a Smith & Wesson on his Facebook page, and had a rap sheet even a veteran street gangster could be proud of.

And now he’s been murdered — at age 14.

Bronx seventh-grader Christopher Duran was stalked and gunned down on a sidewalk near his Bronx home Friday morning — the victim, cops believe, of gang violence.

“He was a gangbanger,” one law-enforcement source said of Christopher, a child known in his Morrisania neighborhood as already well on the road to doom when he was shot dead.

“He terrorized the neighborhood,” said a woman who passed by the grim crime scene.

“Christopher is no good,” another neighbor said.

“I saw him fighting last summer in the street,” the man said. “We told them to quit fighting, but he would not listen. The person he was fighting wanted to quit, but he wouldn’t quit.”

Christopher had been walking to school with his little brother just a few paces from his Sheridan Avenue doorstep when his killer — who had been lying in wait with a lookout posted down the block — pulled a gun.

As the little brother watched, the gunman pumped a single bullet into Christopher’s neck, sources said.

The gunman then stood over the youth’s prone body and blasted away some more, striking the boy multiple times in the torso before he and the lookout both fled.

Christopher was pronounced dead where he lay, in a pool of blood amid eight shell casings cast from a .45-caliber pistol, according to sources.

The boy’s older brother is a “very active leader” in a notorious and violent gang known as 280, law-enforcement said.

Police do not suspect that Christopher was mistaken for his brother.

“You’ve got to believe this guy was specifically targeted,” a police source explained. “You’re not going to confuse this guy with his older brother. It’s believed this guy was purposely targeted, directly targeted.”

Police released video footage of a suspect on Friday afternoon.

“He’s trying to disguise what he looks like,” Chief of Detectives Robert Boyce told reporters. “[He’s wearing] a red bandana. We don’t know what that means just yet. But if you look at that, it’s a very distinctive piece of ­clothing.”

The shooting itself is also on surveillance video but won’t be released because “it’s pretty gruesome,” Boyce said.

Despite his youth, the victim had a lengthy criminal record that includes five arrests — one for an attempted assault with a brick, sources said.

Photos posted to his Facebook page show Christopher flashing what appear to be gang signs. There is also an image of a Smith & Wesson pistol with an extended magazine.

Asked whether he was a good kid who stayed out of trouble, Christopher’s neighbor, Marilyn, 27, replied, “Not really.”

“All I know is he hung out on the block,” she added.

Marilyn heard the gunfire Friday morning as she was getting her own son ready for school.

“When I heard the shots there were four or five, real fast . . . Bang, bang, bang, bang!” she said. “I heard voices yelling, ‘Call the cops! Call the cops!’ When I came out, he was on the sidewalk and people were all around him. Must’ve been 20 people. He wasn’t moving.”

Gerardo Moreno, 19, who lives nearby, described walking up on the hectic scene moments after the shooting.

“All you saw was his mother running out the building, crying hysterically,” he said.

“No mother deserves to go through that. He was a happy kid, always had a smile on his face.

“We would always say what’s up,” Moreno recalled of Christopher. “I’ve known him since he was about 11. It shocks me that such a young kid has his life taken away from him . . . on his way to school.”

Christopher’s uncle, Jesus Mendoza, 29, disputed claims that his nephew was involved in a gang.

“It breaks my heart,” he said, sobbing uncontrollably.

“In the end . . . I want to know why . . . He’s a good kid, nice-looking guy. He never did anything. He never hung out with gangs, nothing like that.”