Sergio Moraes/Reuters

As my colleague Scott Shane reports, American investigators suspect that the two Yemeni-Americans who were detained after the luggage of one was loaded onto a plane he did not board simply “missed their flight on Sunday at Chicago’s O’Hare International Airport after the gate was changed.”

The men were arrested on Monday on board a United Airlines jet in Amsterdam amid concerns that they might have been somehow testing airline security as part of a terrorist plot by sending checked luggage on a flight they did not board. While the men might instead have been innocent victims of heightened suspicion about people traveling to Yemen, the incident is a reminder that more attention is now being paid to what is loaded in the cargo holds of American passenger jets than ever before.

To prevent attacks like the Lockerbie bombing, caused by a suitcase containing a bomb loaded onto a plane without the passenger who checked it also on being on board, airlines are supposed to remove the bags of any passengers who check luggage onto flights they do not board.

In an era of suicide attacks, that precaution no longer seems as reassuring as it once did, but it is still observed carefully enough to trigger alarms like the one on Monday.

But, while all passengers — and their carry-on bags and checked luggage — are screened before they board flights, passenger jets flying into the United States from abroad still routinely carry unscreened cargo, a loophole The Lede pointed out in January.

Asked about the cargo shipped on passenger jets, Nicholas Kimball, a spokesman for the Transportation Security Administration, drew our attention to the fact that 100 percent of the cargo loaded into the holds of passenger jets alongside luggage in the United States is now screened at some stage. In January that figure was said to be “at least 50 percent.”

But in a statement earlier this month announcing that accomplishment, the agency acknowledged that one part of the loophole had yet to be closed: cargo loaded onto jets flying passengers into the country from abroad does not have to be screened.

For cargo loaded onto jets abroad, the federal agency said that it was “continuing its work to improve cargo security on passenger flights originating in other countries. T.S.A. requires 100 percent of high-risk cargo to undergo security screening and has increased the requirements for overall cargo screening.”

The agency’s administrator, John Pistole, said in the statement, “International air cargo is more secure than it has ever been.” He added, “T.S.A. continues to work closely with our international partners and is making substantial progress toward meeting the 100 percent mark in the next few years.”