'Decided to shoot him … over and over': Off-duty security guard stands over teen who was returning a BB gun at sporting goods store and executes him

Aaron Brown Myers (KOMO).

A Washington state man is headed to prison for decades after he shot and killed a 17-year-old boy he claimed was armed and about to commit a robbery but was actually just returning a BB gun to a sporting goods store.

Aaron Brown Myers, 52, was convicted Friday of second-degree murder and assault in the shooting death of 17-year-old Hazrat Ali Rohani outside Big 5 Sporting Goods store in Renton, a Seattle suburb.

Myers faces from just over 20 years to 28 years for the murder plus another 10 years for firearm enhancements, according to the King County Prosecutor's Office.

The defendant, an off-duty security guard, was in his car waiting for his son to finish his martial arts class when he spotted Rohani and two other teens carrying what he believed to be a Glock handgun, according to a probable cause arrest affidavit obtained by The Associated Press. Myers believed the teens were going into the store to rob it.

In reality, prosecutors said, the teens were returning a malfunctioning BB gun. Armed with a real Glock, Myers ran up to the teens and held them at gunpoint.

King County Prosecutor Elaine Lee said the boys repeatedly told Myers that the BB gun was not real. But Myers ignored those pleas.

"The defendant, Aaron Myers, made decisions based purely on assumptions," King County Prosecutor Elaine Lee told jurors, according to a courtroom report from local NBC affiliate KING. "He took one look at these boys walking toward Big 5, carrying a BB gun, and immediately labeled them as criminals."

Lee said Myers gave himself a "self-appointed authority" to detain the teens.

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As he held them at gunpoint, Rohani, who went by Ali, dropped the fake gun and held up his hands.

"When Ali turned to walk away, Mr. Myers decided to shoot him once, twice over and over and over, continuing to shoot as Ali fell to his knees and hands, continuing to shoot as Ali fell face down to the ground," Lee said.

In all, Myers fired seven shots, six of which hit Rohani in the back.

Mark Middaugh, Myers' defense attorney, reportedly told jurors that Myers "needed to act" based on what he saw. Middaugh also noted that the BB gun looked real.

"He didn't want anyone to get hurt," Middaugh insisted. "The reason he got out of his car is he was trying to prevent violence."

But jurors didn't buy the defense and sided with the prosecution.

Myers is set to be sentenced on July 21.