The package addressed to Gov. Martin O'Malley was sent by someone griping about highway signs that urge motorists to call in tips about suspicious activity. A similar package was sent to Transportation Secretary Beverley Swaim-Staley. They were opened within a 15-minute period Thursday afternoon at state government buildings 20 miles apart.
The workers who opened the packages singed their fingers, but there were no significant injuries.
Soon after, mailrooms across Maryland were cleared and two other suspicious packages uncovered, though they turned out to be a toner cartridge and laptop batteries.
"When both packages were opened there was a reaction that caused a flash of fire, a brief flash of fire, smoke and a smell," state police spokesman Greg Shipley told the Associated Press. "This is not to be compared with a significant explosion that you think of when you say that word."
CBS News has learned that one of the packages was addressed to Governor Martin O'Malley at the Governor's mansion but was taken to the state offices at the Maryland Department of General Services' Jeffery Building in Annapolis.
The package addressed to the governor, which injured a mailroom employee, "spit a little flame and smelled of sulfur," when opened the governor told the The Baltimore Sun.
Law enforcement sources tell CBS News that "one device flamed and the other fizzled."
Explosive material wasn't found in either package that ignited and authorities aren't sure if any other dangerous packages are out there, but mailroom employees were back at work Friday. They'll have pictures of the packages and were advised to be vigilant about anything suspicious.
Meanwhile, the packages have prompted officials in at least four nearby states to be more vigilant.
O'Malley, a Democrat, said the mailing sent to him complained about highway signs that urge motorists to "Report Suspicious Activity" and give an 800 number.
"Somebody doesn't like seeing that sign," O'Malley said.
A worker ripped the pull tab on the first package, addressed in typeface to the recently re-elected governor and adorned with holiday stamps, 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.
An administrative assistant to Swaim-Staley opened the second package on the fourth floor of the Department of Transportation headquarters in Hanover, near the secretary's office.
Both had incendiary devices inside and produced puffs of smoke and a smell similar to a match being struck, authorities said.
Maryland's terrorism tip line - the subject of the complaint to the governor - is widely shown on overhead highway signs. The state also uses the signs to post information about missing children and, to the ire of some drivers, added real-time traffic estimates to major highways in March. Some commuters complained drivers slowed to read the signs and backed 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. Postal Inspector Frank Schissler, a spokesman for the Washington division of the inspection service, said Friday that investigators were examining postmarks and other exterior markings on the packages in an attempt to trace their origin.
The postal service also will examine its internal tracking data, Schissler said. Packages are tracked once they enter mail processing plants. But the packages did not have individual tracking numbers because they were sent by first-class mail, not registered mail or express mail, he said.
Schissler also said that DNA analysis was likely. Maryland State Fire Marshal William Barnard said Thursday that numerous pieces of physical evidence were recovered from the scene of the package sent to the transportation department.
A mail carrier was delivering and picking up mail Friday morning at the Jeffrey Building in Annapolis, where the first package was opened, and other state office buildings. Workers met the mail carrier's truck on the street near the governor's mansion to exchange outgoing mail for incoming mail. They declined to comment.
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 terrorist 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.
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.
The Department of Transportation is subjecting mail to additional scrutiny, but otherwise operations were back to normal Friday, spokesman Jack Cahalan said.
After the administrative assistant opened the package Thursday, she dropped it on the floor and someone pulled a fire alarm. Cahalan, who was on the fourth floor but did not see the package being opened, said he initially thought the alarm was a drill. About 250 people work in the four-story building, and the evacuation was orderly, he said.
"I've participated in more fire drills here than I ever did in elementary school," he said. "Everybody knows the drill; everybody knows what to do."
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 what happened and was monitoring. The packages would most likely be taken to an FBI lab at Quantico, Va., to be examined, Barnard said.
Postal inspectors have identified 13 dangerous devices sent through the mail since 2005, and only one person was injured, according to the U.S. Postal Service. Inspectors made arrests in eight of those cases, said Schissler, who noted that the packages sent Thursday would not be classified as dangerous because they did not contain bombs.
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. The anthrax spores killed five people and sickened 17.
O'Malley, speaking after a Maryland Association of Counties dinner, said he had talked 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.