(CNN) All three cases started with a traffic stop.

A black man is pulled over by a police officer.

Why?

He was missing a front license plate. For suspicious activity. Because a cop thought the driver looked like a robbery suspect.

Regardless of the reason, the outcome was the same for Samuel DuBose, Sylville Smith and Philando Castile -- none of them survived.

The police officers fired their weapons, saying they had feared for their lives.

The three shootings were on video, which was scrutinized by lawyers and repeatedly played before the jurors.

All three of these cases came to a head last week without any of the former police officers found guilty. Two were acquitted and one trial ended in deadlock.

Prosecutors haven't had much success convicting police officers in high-profile cases, even when the shooting is on video.

In May, Oklahoma police officer Betty Shelby was acquitted in the shooting death of Terence Crutcher, an unarmed black man.

The lack of convictions has riled advocates and victims' families who say the system is stacked in favor of law enforcement and disregards black lives.