Theorists are making connections to Newtown, Patriots' Day, and Waco.
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:
Via: Charles Krupa, File / AP
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.
Via: Winslow Townson / AP
Here's Wolf Blitzer discussing it: