The challenges in prosecuting police officers

As has been the case with many fatal police encounters in recent years, it is notoriously difficult to prosecute police officers. Just this month, for instance, Tulsa Officer Betty Shelby was acquitted of manslaughter in the shooting death of Terence Crutcher, which occurred just months after Castile's death.

Experts have suggested that despite being presented with video evidence of the shootings, juries — especially those made up of white Americans or middle-class black Americans — are still reluctant to overcome the so-called "halo effect" surrounding police officers that presumes their innocence.

"The interesting thing about video footage is that it's still subject to interpretation," Delores Jones-Brown, a professor at the John Jay College of Criminal Justice, told Business Insider last summer.

"It takes a motivated prosecutor and a good prosecutor to convince whoever they have to convince that what you're seeing on the video is illegal behavior."