Maggie Koerth-Baker in the New York Times:
In the days following the bombings at the Boston Marathon, speculation online regarding the identity and motive of the unknown perpetrator or perpetrators was rampant. And once the Tsarnaev brothers were identified and the manhunt came to a close, the speculation didn’t cease. It took a new form. A sampling: Maybe the brothers Tsarnaev were just patsies, fall guys set up to take the heat for a mysterious Saudi with high-level connections; or maybe they were innocent, but instead of the Saudis, the actual bomber had acted on behalf of a rogue branch of our own government; or what if the Tsarnaevs were behind the attacks, but were secretly working for a larger organization?
Crazy as these theories are, those propagating them are not — they’re quite normal, in fact. But recent scientific research tells us this much: if you think one of the theories above is plausible, you probably feel the same way about the others, even though they contradict one another. And it’s very likely that this isn’t the only news story that makes you feel as if shadowy forces are behind major world events.
“The best predictor of belief in a conspiracy theory is belief in other conspiracy theories,” says Viren Swami, a psychology professor who studies conspiracy belief at the University of Westminster in England. Psychologists say that’s because a conspiracy theory isn’t so much a response to a single event as it is an expression of an overarching worldview.