Deadly 'knockout' game investigated across the U.S.

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A warning -- some of you may find the video disturbing.

The so-called game involves a young person walking up to an unsuspecting passerby and trying to knock them out cold with a single wallop.

Several of the incidents have been captured by surveillance cameras, while others were intentionally videotaped.

Attacks like this have been reported in at least five states, especially in New York and New Jersey.

Two people have been killed by these assaults.

Some of the attacks are being treated as hate crimes. Victims are usually white or Asian.

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