[esad]

We're not seeing the whole video. As was mentioned in the article

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The tape was photographed by an unnamed neighbor who gave it to B. Kwaku Duren, a lawyer who represents Cardenas.

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So, I'm willing to bet that just this segment of the video was released because it only contains a scene that would be damaging to the cops and make his client look good.

Edited to add:

Another part of the article talks about why this happened
[ QUOTE ]
The incident began when the officers spotted Cardenas, a Gordon Street gang member wanted on a felony warrant for stolen goods, and he fled, police said. During the subsequent arrest, a struggle ensued and the officers reported that they used force to subdue the suspect.

[/ QUOTE ]

So, gang member wanted on a felony flees police.