"Right now we don't have any other packages, but we're not taking anything for granted," D.C. Police Chief Cathy Lanier said.
Initial information indicated the parcel that ignited in northeast Washington about 2:45 p.m. was similar to the two packages opened in Maryland on Thursday, authorities said. The Washington postal facility was evacuated after an employee discovered a parcel that looked similar to the Maryland mailings, authorities said. No injuries were reported.
The Maryland packages contained a note railing against highway signs urging motorists to report suspicious activity, investigators revealed.
The message read: "Report suspicious activity! Total Bull----! You have created a self fulfilling prophecy."
At the D.C. facility, which primarily handles mail for the federal government in Washington, workers are not allowed to open packages, postal inspector Frank Schissler said, so it's unclear exactly how the parcel ignited.
The package was "popping, smoking and there was a brief flash of fire," Lanier said, which was very similar to what authorities described in Maryland.
The labels, postmark and stamps were also similar to the Maryland parcels, Postal Service spokeswoman Joanne Veto said.
The D.C. package that ignited was addressed to Napolitano, according to a Homeland Security Department official who spoke Friday on condition of anonymity because it was an ongoing investigation. The postal facility is not near downtown or the Capitol.
The earlier packages, addressed to Gov. Martin O'Malley and to Transportation Secretary Beverley Swaim-Staley, have been taken to the FBI lab in Quantico, Va., for forensic analysis. They did not contain explosive material.
They were opened within a 15-minute period Thursday at state government buildings 20 miles apart.
The workers who opened the packages singed their fingers, but there were no significant injuries. Mailroom employees were back at work Friday, and they had pictures of the packages and were advised to be vigilant about anything suspicious.
Investigators had no previous indication the packages would be sent anywhere other than Maryland government buildings, Wolf said. While Maryland State Police has been the lead investigative agency, the FBI might now be forced to take a more active role, he said.
Police have not yet identified any suspects. Anyone arrested would be charged with possession and use of an incendiary device, which includes a maximum penalty of 20 years in prison, authorities said.
Speaking before the new package was found, Maryland State Police Col. Terrence Sheridan said Friday that authorities were expecting more packages to surface.
"We've got to make sure we go after this person and get them off the street and get them behind bars, because these kinds of things are very, very dangerous," Sheridan said. "We just don't know where this person is going with this. We don't know who it is. We don't know what they're thinking right now."