In Maryland, state and federal officials are investigating two incendiary devices that sent off shots of flames and a scent of sulfur.
"When [the first two] packages were opened, there was a reaction -- a reaction that caused a brief flash of fire, smoke and a smell. This is not to be compared with a significant explosion that you think of when you say that word," says Maryland State Police spokesman Greg Shipley.
The packages went off within 20 minutes of each other, beginning at 12:25 p.m.
One went off at Hanover, at the Maryland Department of Transportation, and the other in Annapolis at the Jeffrey Building just blocks from the Maryland State House –- that one was addressed to Gov. Martin O'Malley.
The packages were shaped like books, and they did not cause any serious injuries. There were complaints of singed fingers by the employees who opened them, but no one was sent to the hospital with actual injuries. A few people were sent just as a precaution.
Both buildings were evacuated: 250 people from Maryland's Department of Transportation, 50 people from the Jeffrey Building. People in the Jeffrey Building did return to work by 3 p.m. However, the Transportation Department headquarters remained empty at 4 p.m.
Maryland State Police, the FBI and the Joint Terrorism Task Force continue to investigate.
A third package found in a state office building in Baltimore was also under suspicion but that investigation has since been closed.
This post has been updated.