Three people were killed and some 140 wounded Monday when a pair of explosions were detonated near the finish line of the Boston Marathon. Police and federal authorities are still investigating the causes and perpetrators of the Boston Marathon explosions, but the timing of the blasts curiously links up to several other infamous events. 

This week marks the anniversaries of the Waco, Texas, siege (April 19, 1993), the Oklahoma City bombing (April 19, 1995), the Columbine High School massacre (April 20, 1999), the Virginia Tech shootings (April 17, 2007) and Adolf Hitler’s birth (April 20, 1889). The Boston Marathon explosions also coincided with the Massachusetts holiday Patriots’ Day and Tax Day, the federal income tax deadline. 

On April 19, 1995, American domestic terrorist Timothy McVeigh and his associates killed 168 people by setting off a truck bomb outside the Alfred P. Murrah Federal Building in downtown Oklahoma City, Okla. The Oklahoma City bombing remained the deadliest single act of terrorism in America until the Sept. 11, 2001, attacks. And its overlap  with the anniversary of Waco, Texas siege is no coincidence. 

Two years earlier, the federal government began a siege of Mount Carmel Ranch outside Waco, Texas. The ranch was used as a compound by the religious group know as the Branch Davidians, and the Bureau of Alcohol, Tobacco and Firearms had reason to believe that the Branch Davidians were violating federal firearms laws. The ATF planned to conduct a quick raid of the property, but an intense gun battle dragged out into a 50-day siege of the ranch. Ultimately, the Waco siege ended on April 19, 1993, after a fire broke out in the Branch Davidians complex, and 83 members of the group died.

McVeigh, a right-wing extremist and Persian Gulf War veteran, blamed the federal government for the Waco disaster and intentionally timed the Oklahoma City bombing to coincide with the second anniversary. 

What does all of this have to do with the Boston Marathon explosions? Possibly nothing. So far, authorities have not made any arrests or announced any suspect or theory about who was behind the bombings. But the tragedy’s close alignment with the Oklahoma City bombing, the Waco siege, and Tax Day have led some media outlets, including Fox, CNN and ABC , to speculate that the Boston Marathon explosions were perhaps intentionally timed to reflect one of these days, just as McVeigh planned the Oklahoma City bombing.

Slate notes that the end of the Waco siege and the Virginia Tech massacre happened to fall on Patriots’ Day in the years they occurred. Patriots’ Day is a Massachusetts holiday celebrating the opening battles of the Revolutionary War in Lexington and Concord. Originally, Patriots’ Day was held on April 19, the actual date of the 1775 battles, but in 1969 , Massachusetts switched the holiday to the third Monday of April. The Boston Marathon has always coincided with Patriots Day.

For now, no one has any idea exactly why the Boston Marathon bombings occurred or who orchestrated these tragic events. But their timing and possible ties to several other American tragedies raises several questions that may never be fully answered.