Missouri police have arrested 31 people after racial unrest rocked Ferguson, following the fatal shooting of a black teen by a white police officer.
Dzhokhar Tsarnaev could be executed if convicted after he was indicted on 30 charges, including that of killing four people.
The trial of accused mobster James "Whitey" Bulger, who evaded the FBI for 16 years before his arrest in 2011, is due to begin in Boston.
Federal prosecutors have charged badly-wounded Boston Marathon bombing suspect Dzhokhar Tsarnaev in his hospital bed.
Boston police commissioner Ed Davis has warned the city of Boston to "shelter-in-place" as authorities pressed a manhunt for the second suspect.
Police have descended on a Boston suburb amid reports of gunfire and explosions after a university police officer was shot dead on the MIT campus.
Two explosions struck the Boston Marathon as runners crossed the finish line, witnesses say, leaving at least 20 injured and two dead.
Floodwater from Hurricane Isaac jumped a levee in New Orleans but the barriers built to protect the city after the Katrina disaster were not breached.
Robert Kiprono Cheruiyot smashed the course record to win the Boston Marathon men's race on Monday, while Teyba Erkesso captured the women's title.
United States Senator Edward Kennedy, a towering figure in the Democratic Party, has died at age 77, his family said on Wednesday.