In ProPublica's latest data analysis, Ryan Gabrielson and Ryann Grochowski Jones discovered a startling truth: black teens in recent years were about 21 times as likely to be shot and killed by police than their white peers.

The reporting duo, along with Eric Sagara, examined more than 12,000 police homicides in the FBI's Supplementary Homicide Report and found that for the risk to be equal, 185 more white teens would have had to be killed at the hands of law enforcement between 2010 and 2012, more than one a week -- a significant racial disparity that cannot be explained away by flaws in the data alone, they explain to ProPublica editor-in-chief Steve Engelberg on the podcast.

So what kind of circumstances are leading police to use deadly force?

For teens who aren't black, most often the victim is alleged to have attacked the officer or somebody else, Gabrielson says. This accounted for about a third of deadly shootings when our country had a more "wild west" approach to law enforcement, allowing police to do whatever was necessary to stop a suspected felon. However, in 1985, the Supreme Court ruled that police could justify using deadly force only if the suspect posed a threat to officers or others. Suddenly, claims of "officer under attack" doubled to 62 percent of police killings.

"If this data is our measure, then assaults on police are apparently increasing at a time when all assaults are just falling to the floor," Gabrielson says.

The other set of instances leading law enforcement to use deadly force involved teens who were said to be fleeing the scene or evading arrest. "How do you fear for your life when someone is fleeing?" Engelberg asks.

We need to dive much deeper into the justifications for these shootings, Gabrielson says. The way that these numbers have changed over the past three decades merits much closer scrutiny.

Listen to this podcast on iTunes, SoundCloud or Stitcher. And read Gabrielson and Grochowski Jones's full report here.