Two packages about the size of small books ignited and released a sulfur-like smell when they were opened Thursday at Maryland state government buildings 20 miles apart, slightly burning the fingers of two employees.
One of the parcels was addressed to Gov. Martin O'Malley, who said the mailing meant for him complained about highway signs that urge motorists to report suspicious activity.
"Somebody doesn't like seeing that sign," the Democrat said.
The fiery devices caused the evacuation of mailrooms at government offices across Maryland. Two other suspicious packages were discovered elsewhere, though one was found to be a toner cartridge, the other laptop batteries.
An official told NBC News that the two packages that ignited contained a message from a disgruntled state employee protesting the state's road signs that urge people to report suspicious activity, stating "you have created a self-fulfilling prophecy."
A federal official told NBC News that the packages resemble dozens sent in late 2004 to governors nationwide — intended to spark a fire when opened.
The devices found Thursday contained a compound similar to what's on a match head, with a battery to create a spark that set them off.
A worker unzipped the first package, addressed in typeface to the recently re-elected governor and adorned with holiday stamps, around 12:30 p.m. in Annapolis where mail for O'Malley's office is routinely checked. The building is just blocks from the governor's office, which is inside the State House in the heart of the capital.
The package contained a message about the state's terrorism tip line, which is widely shown on overhead highway signs that read, "Report Suspicious Activity" and give an 800 number.
The state also uses the overhead signs to post information about missing children and, to the ire of some drivers, it added real-time traffic estimates to major highways in March. Some commuters complained drivers were slowing down to read the signs, backing up traffic. At O'Malley's request, the state studied the issue and removed the real-time postings from one congested area on the Capital Beltway.
U.S. Rep. C.A. Dutch Ruppersberger, D-Md., said a return address on one of the packages turned out to be a Washington parking garage. Ruppersberger, a member of the House Intelligence Committee who was briefed on the mailings, said there were no apparent links to terror organizations.
"I believe this is what we call in intelligence a lone wolf situation, involving an individual who for whatever reason was upset with state government," Ruppersberger said.
The second package, torn open about 15 minutes after the first, was sent to state Transportation Secretary Beverley Swaim-Staley, Ruppersberger said, although he was not certain whether her name was written on it.
It was opened at the agency's headquarters in Hanover, near Baltimore's airport. The woman who burned her fingers at the transportation agency building was taken to a hospital, as were three other people who were concerned because they were near the package when it was opened.
Cate Conroy, acting director of outreach and advocacy for the Veterans Affairs Department, where the governor's mailroom is housed, was in the building when the package was opened. She said employees calmly left while reports of smoke were investigated.
"It happened quite quietly, actually," Conroy said, adding that employees were allowed back into the building a few hours later.
State police were preparing photographs of the two packages for agency mailrooms so they can open Friday, and will provide steps workers should take if they find something, spokesman Greg Shipley said.
The FBI's joint terrorism task force was assisting in the investigation. A U.S. Homeland Security Department official said the department was aware of the incidents and monitoring them. One of the packages would most likely be taken to an FBI lab at Quantico, Va., to be examined, state fire marshal William Barnard said.
Postal inspectors have identified 13 dangerous devices since 2005, and only one person was injured, according to the U.S. Postal Service. Both packages were sent by mail and the agency is also investigating.
In 2001, as the nation was still reeling from the 9/11 attacks, letters containing anthrax were sent to lawmakers and news organizations. Postal facilities, U.S. Capitol buildings and private offices were shut for inspection and cleaning by workers in hazardous materials suits. The anthrax spores killed five people and sickened 17.
At the height of the furor, other suspicious packages were reported at the Maryland Department of Health and Mental Hygiene headquarters in Baltimore and the city courthouse. One contained a toner cartridge, while the other was laptop batteries.
O'Malley, speaking after a Maryland Association of Counties dinner, said he had spoken with one of the workers injured by the packages and left a message for the other, and they were doing fine.
"I think it just underscores how whether it's the mail or whether it's the subway system or an airline, in this age ... you just have to be very, very vigilant because our openness and the freedom with which we communicate and with which we travel can be used as weapons against us," he said.