1. Part of the marathon was dedicated to Newtown victims.
Many have pointed out that the Boston Marathon was honoring the victims of the 2012 shooting in Newtown, with a special marker at the 26th-mile mark. That’s just 0.2 miles from the race’s end, where the explosion took place. According to ESPN, the 26th-mile spot has significance because of the 26 killed at Sandy Hook.
Some reports also say that Newtown families may have been at the finish line, though we have been unable to confirm that claim:
2. The history of violence on Patriots’ Day.
Monday is Patriots’ Day in Massachusetts, which commemorates the Revolutionary War battles of Lexington and Concord. Public schools have the day off, and a Red Sox game typically takes place in the morning.
Here’s Wolf Blitzer discussing it:
3. The Waco siege ended on Patriots’ Day.
On April 19, 1993.
4. Contrary to some claims on Twitter, the Oklahoma City bombing did not take place on Patriots’ Day.
Patriots’ Day was on April 17 that year. The bombing in Oklahoma City was two days later, on April 19.
Bomber Timothy McVeigh’s letter and explanation on that here.
5. There’s rampant speculation — but so far, only speculation — that the explosion could be either an al-Qaeda attack or a “right-wing extremist” assault.
CNN’s senior national security said investigators should pay attention to what kind of explosives are used: “If it was hydrogen peroxide, this is a signature of al-Qaeda. If it was more conventional explosives, which are much harder to get ahold of now, that might be some other kind of right-wing extremists.”