What makes a package look like trouble?

According to the US Postal Service, signs (pdf) to look out for include any of these indicators:

Private shippers like FedEx and UPS rely on what they describe as a “risk-based strategy,” and “hope to detect illegal or dangerous shipments by spotting something unusual about the package or the shipper,” according to the Associated Press. Neither company would discuss details but said they do cooperate closely with law enforcement.

US government offices are especially vigilant. “At the FBI we had an intake procedure for every package that came in,” former FBI agent Dana Ridenour told Quartz. “They were scanned, they’d go through a metal detector, all before they really got inside.”

The federal warnings to companies

The US Department of Homeland Security tells corporations of all sizes that “mail screening is both an art and science.”

There are “no guarantees that even the best screening technology and procedures will identify all potential threats before a letter or package arrives at the desk of the intended recipient,” says a guide distributed by the agency to the public and private sector.

“Threats in the mail stream are continually changing,” the DHS handbook instructs. “New explosives, new electronic trigger devices, and new biological and chemical substances are appearing at more frequent intervals. Nuclear proliferation is making radioactive materials potentially more available than ever before. Terrorists are hiding explosives in common office supply items and electronic devices, making them increasingly difficult to detect. Loading docks and delivery vehicles often provide easy access to buildings that have high levels of security screening at their lobby entrances.”

Don’t use your cell phone near a suspected device, the FBI warns. Get out of the immediate area, then call 911.

“Package bombs, which include letters, parcels, and anything delivered by postal or courier service, are not a new technique and have been used by terrorists and anarchist groups,” says a bulletin (pdf) from the FBI’s National Explosives Task Force. “Many of these bombs are triggered when victims handle or open the packages, although they can be initiated in other ways.”

Today, the FBI issued a statement warning Americans to be on guard, CNN reported: “It is possible that additional packages were mailed to other locations. [Do] not touch, move or handle any suspicious or unknown packages.”

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