A gunman opened fire at two military facilities on Thursday in Chattanooga, Tennessee, killing four Marines and injuring at least three other people. Officials confirmed that the shooter is deceased following a police pursuit.

“We are treating this as an act of domestic terrorism,” said U.S. Attorney Bill Killian in a news conference Thursday afternoon. The shooter has been identified as 24-year-old Muhammad Youssef Abdulazeez of nearby Hixton, the Associated Press reports.

The shootings began at approximately 10:45 a.m., when gunfire erupted outside an Armed Forces Career Center on Lee Highway, six miles east of downtown Chattanooga. No fatalities occurred at this location, according to to FBI Special Agent Ed Reinhold.

Chattanooga Police then pursued the suspect to a U.S. Naval Reserve Center located seven miles away, where four victims and the shooter were killed. Several other people suffered nonfatal gunshot wounds, including a police officer who was shot in the ankle.

“This is a nightmare for the city of Chattanooga,” said Mayor Andy Berke.“It is incomprehensible to see what happened and the way that individuals who proudly serve our country were treated.”

The active-shooter situation ended “within 30 minutes” of the shots being fired outside the recruiting center, according to Reinhold. He declined to say whether the shooter was killed by law enforcement or took his own life, and said only that the shooter used “numerous weapons.” The shooter did not work at either of the facilities, he added.

Reinhold also appeared to walk back Killian’s classification of the shootings as domestic terrorism. “We are looking at every possible avenue,” he said. “Whether it was terrorism, whether it was domestic or international, or whether it was a simple criminal act.”

If the shootings are ultimately tied to terrorism, it would perpetuate a pattern that has emerged in terrorist attacks on U.S. soil in recent history. Writing for The Trace, researcher Louis Klarevas, using open-source databases and press reports, determined that (as of June 30) 142 incidents of domestic terrorism have taken place in the country since 2002.

Among those incidents, he writes:

The most common type has been ecoterrorist attacks associated with left-wing ideologies, the vast majority of which were intended to make a political statement without injuring anyone. Only two left-wing attacks have resulted in fatalities.

The attacks emanating from the other side of the political spectrum, while fewer in number, have drawn more blood. There have been 11 lethal strikes by right-wing terrorists, many of them either Christian fundamentalists or white supremacists, resulting in 29 deaths.

A third category includes jihadist and nonpartisan antigovernment attacks. These accounted for the remaining 11 incidents and represent the deadliest subcategory, resulting in 54 fatalities. In relative terms, jihadists have claimed more lives per attack than any other group, killing 23 people in just five incidents. This is largely the result of Nidal Hasan’s bloody rampage at Fort Hood, which took the lives of 13 people in 2009.

In all, since 2002 there have been 24 deadly acts of terrorism on American soil. Combined, they have claimed 86 lives, an average of 3.6 lives per attack.

These are all illuminating statistics, but arguably the most profound takeaway comes from an analysis of which types of weapons are responsible for killing Americans during the commission of political extremism. Unambiguously, the deadliest means of terror in the post-9/11 United States has been the gun. Firearms, indeed, have been used in all but one of the lethal terrorist attacks perpetrated since 2002 — the exception being Joseph Stack’s aerial assault on the IRS offices in Austin, which killed an employee of the tax agency. Even the Boston bombers used a handgun to kill one of their four murder victims.

In the final count, firearms have claimed 82 of the 86 lives lost as a result of domestic terrorism since 2002.

(Photo: Tim Barber/Chattanooga Times Free Press via AP)