Jake Pearson at the Associated Press reports that a medical examiner found the chokehold is what killed Eric Garner:

Eric Garner, 43, whose videotaped confrontation with police has caused widespread outcry and calls by the Rev. Al Sharpton for federal prosecution, was killed by "the compression of his chest and prone positioning during physical restraint by police," said medical examiner spokeswoman Julie Bolcer.

Let's be clear about what this means: That video shows a homicide in progress.