Verification of this is lacking but it does sound plausible.  I really need to write up a proposal for the lab where I work and try to do a valid research project on airplane security alternatives.  Everyone knows the current system is a total failure.

From Ms. Malkins post:

He and his partner were assigned to a flight (the airline, airport, and destination were not disclosed) in their customary undercover security role. They boarded the airplane early in order to meet the flight attendants, at which time the cleaning crew was still on the airplane — somewhat longer than expected. My patient and his partner sat together in seats near the middle of coach class.

The passengers began to board, and he and his partner noticed a single Middle Eastern man sitting near the front of first class. After a number of passengers had boarded, two Middle Eastern men walked by this man and made eye contact, but said nothing. They sat down together in the front of coach class. Shortly thereafter, two other Middle Eastern men also walked by the man in first class and made eye contact without speaking. They sat near the back of coach class.

Shortly after the flight attendants completed their post-boarding check of the overhead bins, an announcement came from the cockpit: the pilot stated that there had been a security breach, and everyone needed to deboard the plane for a second, more thorough, security screening. The Air Marshall and his partner were confused, as they had not triggered the security alert nor been notified of it prior to the announcement.

After all the passengers had deplaned, the Federal Air Marshalls checked with the flight attendants for more information. During a final check of the overhead bins, a flight attendant had noticed that one of the blankets was slightly unfolded, and he repositioned it in the bin. At this time, a razor blade fell out of the blanket. Concerned, but still believing this might be a straightforward mistake, the flight attendant began to check other overhead bins. Several additional incompletely folded blankets were noted, and hidden in each one was a box cutter: a total of five. It appeared that these had been placed there by the cleaning crew prior to the boarding of the airplane.

After the repeat security screening, the passengers reboarded — all except the five Middle Eastern men, who were nowhere to be found. The flight proceeded to its destination uneventfully.