The shooting in San Bernardino is part of the collection of such incidents to happen in the U.S. this year.

When it comes to active shootings, what patterns emerge when it comes to who is behind them, and when they happen? J. Pete Blair is the executive director of the Advanced Law Enforcement Rapid Response Training Center (ALERRT) at Texas State University. He is also the co-author of the FBI's active shootings report. He joined the show to breakdown what the FBI has learned about active shootings.

Mass shooters vs. active shooters: They aren't considered to be interchangeable, Blair said. "Probably the easiest way to think about an active shooter incident is it's an attempted mass murder," Blair said. "And we don't put a limit on the amount of people shot or killed, because we think we can learn as much from incidents where very few people were shot or killed as we can from incidents where a lot of people were shot and killed."

In the last five years, there have been an average of 18 active shooting events per year: "The median number of people shot per event is four," Blair said. When it comes to the number for 2015, Blair said the FBI is still evaluating the data.

The demographic tends to be male: "Outside of that, we see attackers from every major racial and ethnic group in the United States, and about in their proportion with their representation in the population," Blair said, adding that the ages in the FBI dataset range from 13 to mid-80s.

Active shootings typically happen during business hours: That's when people will be there, Blair said. The FBI has not found a pattern in a typical day of the week that active shootings occur.

To hear more about what the FBI knows about active shootings, click on the blue audio player above.