Okay... nothing to go on but this article....
I know 90 rounds seems excessive, and the 'unarmed teenager' thing sounds over the top as well. It sounded thus to me, before I thought about it a while.
The man said he had a weapon, said he would use it, and the video clearly shows the guy putting himself into firing stance. Ya... I would have lit his ass up as well.
Now, 90 round? 90 rounds? Yes, I can buy that too. It's not nice, not pretty, and frankly would be embarrassing as hell to a professional.... or should be. That said, what it really means is half a dozen poorly trained officers unloading a magazine each.... at night, at longer range, while their world opens up into muzzle flashes and bigum bangums all around them.
The article reads like some wiley coyote supper genius decided to commit suicide by cop.... and it worked.