Suspicious letter addressed to US President Obama has tested positive for the deadly poison ricin, as did a letter to a Republican Senator.
The FBI assessment is that there are no links between the poison letters to Obama and Senator Roger Wicker and the bombs at The Boston Marathon.
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An 'unarmed' black man, who was reported to be mentally ill, has been shot dead by police in California after his sister called for help.
"Rubble fell in on intensive care patients" in the early hours of Wednesday, medics said.
The inquiry's most senior lawyer is said to be considering stepping down after disagreeing with its chairwoman Alexis Jay over its future.