More than two dozen people were killed this weekend in two mass shootings in the United States.

At least 20 people were killed Saturday as a gunman walked through an El Paso, Texas, Walmart shooting randomly at shoppers, then went to the parking lot and continued firing until he surrendered to police.

Thirteen hours later, a man who was clad in body armor shot three dozen people in a Dayton, Ohio, neighborhood in less than a minute, killing nine and injuring more than 20 others. One of his victims was his sister, according to law enforcement authorities.

The man’s motive for the shooting is not yet known.

The El Paso shooting will be treated “as a domestic terrorist case," according to John Bash, U.S. Attorney for the Western District of Texas. The attack, Bash said at a news conference Sunday, fit the definition of a hate crime since it appeared "to be designed to intimidate a civilian population, to say the least".

According to law enforcement authorities, the alleged El Paso shooter, Patrick Crusius of Allen, Texas, is believed have posted a text on 8chan, an online message board frequently used by many far-right groups, around 20 minutes before the shooting began in El Paso.

The four-page document, reportedly littered with racist rants and screeds against a “Hispanic invasion,” also included messages of support for the gunman who killed 51 people in Christchurch, New Zealand, in March.

FBI Director Christopher Wray testified before Congress last month that a growing number of domestic terrorism arrests in the past nine months had been linked to white supremacist violence.

”I will say that a majority of the domestic terrorism cases that we’ve investigated are motivated by some version of what you might call white supremacist violence, but it does include other things as well,” Wray said at a Senate Judiciary Committee.

What is a hate group, where are they and is anyone monitoring them?
Here's a look at the growing number of cases involving shooters who have avowed sympathies with white supremacist groups.

What is a hate group?

A hate group’s "primary purpose is to promote animosity, hostility, and malice against persons belonging to a race, religion, disability, sexual orientation, or ethnicity/national origin which differs from that of the members of the organization,” according to the FBI.

Does anyone monitor hate groups?

The FBI tracks hate crimes and publishes a yearly report on hate crimes by state.

While the department tracks individuals and hate groups, it does not publish a public list of the groups.

According to the FBI, the agency says, “Investigations are only conducted when a threat or advocacy of force is made; when the group has the apparent ability to carry out the proclaimed act; and when the act would constitute a potential violation of federal law."

In the annual hate crime report released last November, the FBI listed 7,775 criminal incidents for 2017. That was up from the 2016 number of 6,121 incidents and was the third consecutive year the numbers had gone up.

The Southern Poverty Law Center has also reported a surge in the number of white nationalist groups in the past year.

The SPLC is a nonprofit group that tracks hate organization in the United States. The SPLC's Hate Map is compiled using material scanned from hate group publications and websites and law enforcement reports.

The SPLC’s reporting is broad and includes material presented in speeches, meetings, rallies and published material. As of the time of the Dayton shooting early Sunday, the Hate Map listed 1020 active hate groups.

The SPLC has been criticized for the inclusion of some groups on the list and has been sued over the listing. The extremist group label has been placed on such groups as the American College of Pediatricians (for its stance on LGBTQ issues), Catholic Family Ministries (listed as a "general hate group") and the Conservative Republicans of Texas, which the SPLC says is anti-gay.

The Simon Wiesenthal Center's Digital Terrorism and Hate Project follows the activities of hate groups that are carried out and those talked about online.

What is a hate crime?

A hate crime is one motivated by bias against someone because of their race, religion, disability, sexual orientation or other characteristics, according to the Department of Justice.

Are there any states that have not enacted hate crime laws?

These states do not have state hate crimes on the books, according to the Department of Justice:
Georgia
South Carolina
Arkansas
Wyoming

These states have hate crime laws, but do not require reporting of hate crimes to the FBI:
Alabama 
Alaska 
Colorado
Delaware 
Kansas 
Mississippi 
Missouri
Montana
New Hampshire
North Carolina
North Dakota
Ohio
South Dakota
Tennessee
Vermont
West Virginia
Wisconsin

These states have hate crime laws and require that hate crimes be reported to the FBI.
Arizona 
California 
Connecticut
District of Columbia
Florida
Hawaii
Idaho
Illinois
Indiana
Iowa
Kentucky
Louisiana
Maine
Maryland
Massachusetts
Michigan
Minnesota
Nebraska
Nevada
New Jersey
New Mexico
New York
Oklahoma
Oregon
Pennsylvania
Rhode Island
Texas
Utah
Virginia
Washington

What is the difference between federal hate crimes and state crimes?
The shooters in both of this weekend's incidents would face state charges for the shootings.

Texas authorities Sunday filed a capital murder charge against Crusius. The Dayton shooter, Connor Betts, 24, was killed at the scene.

Federal charges, when they are filed after such shootings, do not supersede state charges.

What does "nexus to a hate crime" mean?
The term "nexus to a hate crime" has been heard in reference to the El Paso shooting. The term means that the manifesto authorities believe the shooter wrote shows his motive was likely linked to a hate group.