My impression, too. Stop the blood flow and the brain dies.
Freeper’s are using “no traumatic asphyxiation” to defend the cop, but that term refers to a crushing chest injury, so it’s meaningless in the context of the other knee being on the side of the man’s neck.
A subtle and lengthy strangulation by constriction of one artery from the knee to the neck would not necessarily leave physical evidence like bruising or petechiae so the lack of evidence is not proof it didn’t happen.
And the video is evidence that it did.