LAS VEGAS -- A Las Vegas Metro police officer was found justified in the shooting of a 15-year-old boy who he claimed was threatening his mother with a knife.

Video: Inquest Shows Officer Shooting Justified

The decision was reached by a coroner’s inquest jury just after 1 p.m. Friday.

Officer Derek Colling shot Tanner Chamberlain in the head Sept. 29, after the boy and his mother fought outside their home at the Sunridge Apartments, near Nellis Boulevard and Vegas Valley Drive.

Chamberlain’s mother, Evie Oquendo, said her son suffered from bipolar disorder, and told FOX5 she pleaded with Colling not to shoot her son.

"They could have Tased him. This cop murdered him and he needs to pay for this!" Oquendo said.

Photos: Teen Shot By Police

Oquendo said she had finally convinced him to take his medicine just before officers arrived. But when Colling ordered Chamberlain to put down a knife he was holding, police said he refused and “made a sudden movement” that forced Colling to pull the trigger.

“They said it once, ‘Drop the knife,’ and I said ‘Don’t shoot,’” Oquendo said. “The next thing I know they shot him right in his head.”

“He was scared and he jumped and he just put [the knife] toward me,” she said. “He wasn’t going to hurt me.”