A Transportation Security Administration (TSA) “information” circular noting a pattern of suspicious objects in airline passenger bags—most notably cheese or clay packed with wires and other electronic equipment—was leaked to the press earlier this year, drawing mixed reactions from security experts about what the discoveries really mean and how the agency handled them.

There were four incidents. First, on September 16 of last year, screeners at Maryland’s Baltimore-Washington International Thurgood Marshall Airport (BWI) spotted a block of cheese packed with a car-charging adapter, for either a cellular phone or portable DVD player in a checked bag.

On November 8, 2006, screeners at Houston’s George Bush Intercontinental Airport spotted a 9-volt battery, wires, pipes, and a block of brown, clay-like material in a checked bag. Similarly, on June 4 of this year, screeners at Milwaukee’s General Mitchell International Airport found a carry-on containing a wire coil wrapped around a possible initiator, an electrical switch, batteries, three tubes, and two blocks of cheese.

The incidents are troubling because terrorists have been known to use such “dummy” objects to check out security responses.

Of the four, the last incident, which occurred at San Diego International Airport, is most clearly benign, though the accounts of locals and the federal authorities differ. The TSA reported that a woman’s bag contained two reusable plastic ice packs, emptied of their original gel contents, filled with clay, and duct-taped together. But San Diego Harbor Police Chief Kirk Sanfilippo told Security Management that the packs contained only ice gel and that household transparent tape—not duct tape—was used, and only to patch holes in the individual packs, the same explanation the traveler herself gave to national media.

In the BWI incident, the Maryland Transit Police spokesperson Cpl. Jonathan Green says that the man and woman possessing the bag were questioned, and it was determined that they posed no threat, so the items were returned to them. No explanations were forthcoming in the other two cases, which seem the most worrisome. Local authorities in Houston and Milwaukee directed all questions to the TSA.

Agency spokeswoman Amy Kudwa would only state generally that in any case where screeners find suspicious items, they determine the bag’s owner, collect his or her personal information, and refer the case to a law enforcement agency, specifically the FBI.

The FBI investigated each case twice, says agency spokesman Special Agent Rich Kolko: first immediately afterward, and again after issuance of the TSA circular. Investigators found no link to terrorism in any of the four cases, Kolko says.

Despite the FBI’s findings, Michael Boyd, an aviation consultant and president of the Boyd Group, believes the objects demonstrate probing by would-be terrorists, albeit perhaps rank amateurs compared to the al Qaeda cells that carried out the 9-11 attacks. It makes one wonder “how many others are there?” says Boyd.

Charlie LeBlanc, former security executive with Continental Airlines and now president of the risk management firm ASI Group, says he has “seen it all” in passenger carry-ons—from harmlessly odd objects to restricted items like handguns, the latter once planted in a bag by a spiteful spouse.

While LeBlanc places full faith in the FBI’s finding, he noted that in his experience, travelers questioned about odd items usually have a simple explanation. “The one thing that concerned me was that when questioned, according to the circular, these people didn’t have a good explanation,” he says.

One potentially positive aspect of the information—it does show that airport screeners caught these items.

Consultant Douglas R. Laird, Sr., CPP, of Laird & Associates, Inc., and former head of security at Northwest Airlines, said the discoveries “speak positively of the TSA, and more importantly the technology they’re using.”

Laird pointed out that the finds were made using explosives detection system (EDS) machines. The large, belt-fed machines scan bags in slices like a medical imaging machine. Then, using software analysis and data about known threats, the machines alert screeners to suspicious items.

EDS machines, however, are only in use at larger airports, Laird says. At smaller airports, the TSA uses explosives trace detection machines, which chemically test swabs taken by hand from the inside of bags.