A stacked deck
He might keep in mind that US police have very strong and intractable unions; the trial prosecutor's career depends on police cooperation for any degree of career success; and typical trial judges are bound to honor the "system as it is" ... many are elected and dare not anger their constituent voters. There's a solid reason why police brutality and criminality is so deeply entrenched in the failed US system of justice.
Other than that, I wish Mr. Afshar every success.
PS: There's also a solid reason why most Americans no longer stop to render aid. Between the cops and the lawyers, it's a risky endeavor. Imagine the "Good Samaritan" beaten, arrested, and prosecuted for his efforts.