During a court hearing today, FBI investigators said they found no traces of ricin at the home or car of a Mississippi man suspected of sending letters laced with the poison to two public officials and President Obama.
Twenty years ago, federal agents clashed with David Koresh's Branch Davidian community near Waco, Texas. The standoff ended with a raid and fire that killed some 80 people. It's remembered as one of the darkest chapters in American law enforcement history.
Two decades later, some of the Branch Davidians who survived the raid are still believers, while a new church group has moved onto the land.
President Obama said the FBI is investigating Monday's twin bombings at the Boston Marathon "as an act of terrorism." Meanwhile, law enforcement officials are asking the public to submit photos and videos from the scene. And Boston Mayor Tom Menino said that as the city grieves the victims it is also proud of those who helped in the explosions' aftermath.