Conspiracy theories about missing or dead scientists boil over

Speculation about links among a handful U.S. scientists who have died or disappeared in recent years was largely confined to niche online communities less than two months ago.

As of Friday, the number had grown to at least 12 and was at the epicenter of U.S. government, with both the FBI and Congress investigating possible connections.

The details vary by case, but tend to suggest that individuals were targeted because of the sensitive nature of their work related to topics such as astrophysics, nuclear weapons and pharmaceuticals.

But so far no evidence has been found that definitively links the cases or establishes coordinated foul play.