Following any violent event, the most intriguing and perhaps important point of study is why something occurred. In a search for meaning, analysts and investigators may find a method for preventing future tragedy, and in counterterrorism and homeland security, one factor is whether the date of an attack has relevance.

Bad things happen every day, and anniversaries of tragic events arise year round. Each month holds a list of significant dates relevant to various extremist ideologies and terrorist groups. Yet, April’s significant events are found largely in the third week, from the 14^th through 20^th. The disproportionate number of incidents in this time period is thought provoking. Consider some examples from April’s history of violence:

April 14:

President Abraham Lincoln was shot in Ford’s Theater in 1865. Assassin John Wilkes Booth famously shouted “Sic semper tyrannis,” his motivation for the attack being a response to the Civil War, which was coming to an imminent end.

While an attack did not occur, it is worth noting that in 1988, Yu Kikumura, a member of the Japanese Red Army terrorist group, plotted to bomb Manhattan, N.Y. He was arrested two days before his planned attack, which he said was to coincide with (and was in retaliation for) a 1986 U.S. air raid in Libya.

April 15:

Two weeks ago, Tamerlan and Dzhokhar Tsarnaev placed pressure-cooker bombs near the Boston Marathon finish line, killing three people and injuring nearly 200. Investigators are still piecing together why the brothers launched the attack.

April 16:

A letter laced with ricin, addressed to Sen. Roger Wicker (R-MS), was intercepted at a mail screening facility. The FBI recently arrested James Everett Dutschke, who has been charged with producing the poison and using it as a weapon of mass destruction. The reason for the attack is not yet known.

In 2007, Seung Hui Cho went on a shooting spree at the Virginia Polytechnic Institute, killing 32 people. Cho was reportedly mentally ill, making his motivation inherently irrational to some degree. In a later discovered video, however, Cho did refer to Columbine High School shooters Eric Harris and Dylan Klebold as “martyrs.”

April 18:

This year, a second letter laced with ricin was intercepted, addressed to President Barack Obama. As with the letter to Sen. Wicker, James Dutschke has been charged.

A suicide bomber drove a car bomb into the U.S. embassy in Beirut in 1983, killing 63 people. This was a turning point in how extremist groups directed their violence, seeing the impact asymmetric warfare can have on larger military forces.

April 19:

In 1775, battles at Lexington and Concord marked the start of open armed conflict in the U.S. Revolutionary War.

In 1993, the FBI inserted tear gas canisters into the Branch Davidian’s Waco, Texas compound in an attempt to force an end to a 53-day standoff. A fire started that engulfed the compound, killing many of the people inside.

In 1995, Timothy McVeigh parked a truck bomb in front of the Alfred P. Murrah Federal Building in Oklahoma City, Okla. The attack killed 168 people. McVeigh later sent a letter to Fox News calling the bombing retaliation for government actions.

April 20:

In 1999, Eric Harris and Dylan Klebold attacked Columbine High School in Colorado, using an arsenal of guns and homemade bombs. They killed 13 people and injured 21 others before killing themselves.

 

Do Anniversaries Matter?

There is sometimes a tendency to over-analyze tragic events, looking for meaning where perhaps there is none. There have not been large-scale domestic attacks whose timing has been linked with, for example, Lincoln’s assassination or the Beirut U.S. embassy bombing. That these events occurred during the third week of April is a matter of coincidence.

Yet anniversaries of violent events do attract extremists. The April 19 final raid on the Branch Davidian compound, as well as the start of the Revolutionary War, were factors in Timothy McVeigh’s timing for his bombing of the Oklahoma City federal building. Years later, the Columbine shooters had McVeigh in mind when launching their assault on a high school, though not because they shared McVeigh’s motivation. Rather, they sought to emulate and even surpass the spectacle and attention he garnered through his attack. And the Columbine shooting was a source of inspiration for Seung Hui Cho’s April 16 attack at Virginia Tech.

Violent extremists often plan their attack to coincide with a significant date, such as an anniversary or holiday, because it can add meaning and exposure to their action. Sometimes a terrorist only has a tenuous grasp of their professed ideology. In a U.S. Air Force Air University study, “A Military Guide to Terrorism in the Twenty-First Century,” the authors write “while some groups will be seriously committed to their avowed ideologies, for others, ideology is poorly understood and primarily a rationale used to provide justification for their actions to outsiders or sympathizers.”

Anniversaries can help legitimize and associate an attack with a larger cause, perhaps better than the terrorist’s own words, which may betray their ideological ignorance. It can provide a kind of justification for an extremist’s desire to do violence.

Violent attacks can also capture greater public interest when they coincide with a significant date. Following the Boston bombing, journalists and commentators zeroed in on April 15 as Patriot’s Day, a primarily Bostonian holiday. To be sure, the bombing would have dominated public attention without the holiday, but given what is being learned about the Tsarnaev brothers, it seems the date could have had significance in their planning.

Yet most terrorist attacks (domestic or foreign) are black swans – inherently unpredictable. If they could be foreseen, they would be more easily prevented. New York City law enforcement would not have expected Japanese Red Army terrorist Yu Kikumura to select Manhattan as a target for retaliation for a U.S. air raid on Libya two years earlier. NYC’s size and international visibility make it a target regardless of the date, as evidenced by the numerous failed and successful attacks on the city.

Beyond this, focusing on significant dates may obscure more relevant factors in terrorist planning. Paul Pillar, former CIA National Intelligence Officer for the Near East and South Asia and a professor at Georgetown University’s Center for Security Studies, writes that there is too much emphasis placed anniversaries:

“Over-emphasis is placed on the date of an attack and on what it might be the anniversary of. This also overlooks the opportunism involved in most terrorist operations, in terms of when, as well as where, it might be most feasible to mount an attack. In general, western analysts and commentators on terrorism devote more attention to anniversary dates than terrorists do.”

Indeed, law enforcement and counterterrorism professionals can likely find more success assessing and securing vulnerable targets than by anticipating the date on which soft targets will be attacked. Yet, it is not simply an academic exercise to determine after the fact what relevance a date holds for a terrorist. It can be valuable intelligence that feeds into the overall effort to prevent terrorist action. Given the history of large-scale violent incidents, the third week in April merits caution. Terrorism can occur on any day, although evidently, some days more than others.