On his way out the door as Attorney General, it turns out Jeff Sessions had a surprise.

He left behind this memo, and it's going to change the way the Department of Justice does business.

But before I explain this memo, before I explain why it's so important, I need to give you a little history.

We're going to go back to 1991, early March, Los Angeles.

Now the story that might never have surfaced if someone hadn't picked up his home video camera.

We've all seen the pictures of Los Angeles police officers beating a man they had just pulled over.

The city's police chief said today he will support criminal charges against some of the men.

Here's ABC's Gary Shepard.

Before cell phone cameras and Facebook Live,

there was this shaky home video of Rodney King.

The three police officers facing felony criminal charges

were among a group of 15 who stopped a 25-year-old black man

last Saturday night, then beat him, kicked him, and clubbed him,

unaware that an amateur photographer was recording the incident on videotape.

Some people have called this tape the first viral video.

And almost immediately, there were calls for action against individual police officers and also against the entire LAPD.

But there was this nagging question. Who polices the police?

In the wake of the Rodney King beating in the video, I think there was a feeling,

essentially sort of two feelings. This is Ian McDougal. He writes for ProPublica.

One was, although some of the officers ended up ultimately going to prison, it's very hard

to prosecute people, officers, for civil rights violations just because of the way the laws

are structured.

...