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.
Mayor Thomas Menino, who is recovering from a broken leg unrelated to the bombing, watches on as President Obama speaks during an interfaith healing service last week following the Boston Marathon blasts.
Tucson Mayor Bob Walkup poses with then-U.S. Rep. Gabrielle Giffords during a Salvation Army fundraiser about a year before she was shot in the head.
Credit Brandi Jade Thomas / AP
Minneapolis Mayor R.T. Rybak and President George W. Bush tour an area near a collapsed interstate bridge, which left 13 people dead in 2007.