He got out of his car with gun drawn.
As the perp is walking toward the squad car as it is pulling up, you can see him drawing his knife, unfolding it with a flick of his wrist (requires practice) and is holding it in a threatening manner. As the cop on the shotgun side opens his door and gets out you can see he has his gun drawn. One can opine he was probably telling the perp to either "drop the knife," or "get on the ground," or words to that effect. When the perp ignored his command, he was stopped from fleeing the scene with a deadly weapon and becoming a deadly threat to other innocents.
Case closed. Gene pool cleansed.
BTW, you won't hear Hannity or O'Reilly with this kind of politically incorrect analysis.
"All that the South has ever desired was that the Union, as established by our forefathers, should be preserved, and that the government, as originally organized, should be administered in purity and truth." – Robert E. Lee
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