Like I said yesterday, it was curious that there was nothing in ABC’s report suggesting that they’d committed a crime. Although I’d still love to know the explanation for taping a cell phone to a bottle of Pepto Bismol.

The U.S. does not expect to charge the men, a law enforcement official said. The two men arrested in Amsterdam — both traveling to Yemen — did not know each other and were not traveling together, a U.S. government official said…

Both of the detained men missed flights to Dulles International Airport from Chicago, and United Airlines then booked them on the same flight to Amsterdam, the U.S. government official said. The men were sitting near each other on the flight, but not together…

Kip Hawley, the former Transportation Security administrator, said it is not unusual to find items like watches and cell phones bound together on flights to countries like Yemen. He said this would always catch the screener’s eye. In 2007, TSA alerted screeners that suspicious items found at U.S. airports may indicate that terrorists were conducting dry runs. Screeners are deliberately on the lookout for such items…

Al Soofi was questioned by the U.S. Transportation Security Administration as he went through security in Birmingham, Ala., Sunday on his way to Chicago, one of the officials said. He told the authorities he was carrying a lot of cash. Screeners found $7,000 on him, but he was not breaking any law by carrying that much money. It is not unusual for people to carry large amounts of cash when they travel to third world countries.

The magic word here, of course, is “Yemen.” Once the luggage went one way and the two of them went another, the alarm bells about their final destination started ringing — even though it looks like it was the airline’s screw-up, not any deliberate act by al-Soofi, that put his bag on the wrong flight. Another factor here is that U.S. aviation security has been on high alert for a terror attack over the past few weeks, replete with lots more air marshals onboard international flights — including the one to Amsterdam:

As a result, air marshals were onboard a Chicago-Amsterdam flight yesterday and kept a close watch on two suspicious passengers who had triggered security alarms, but were allowed to travel for “investigative purposes,” law enforcement sources told ABC News…

U.S. officials said the two appeared to be travelling with what were termed “mock bombs” in their luggage. “This was almost certainly a dry run, a test,” said one senior law enforcement official.

How common are dry runs really, though? A European counterterror official tells Time:

The official says he couldn’t recall dry runs in any of the scores of cases he’s worked on. “Rehearsing an attack runs the considerable risk you’ll be caught without ever being able to attempt the strike — which is the only goal of terrorists,” he says. “If you’re determined to strike and have chosen your method, you’d be better off taking your chances, since success isn’t even an option if you don’t try. Testing the terrain simply increases the risk you’ll be caught without ever really have constituted a threat.” Most would-be terrorists, he says, go through painstaking, detail-obsessed planning in the shadows to increase their chances of success once they go into action — though that sort of sweating the small stuff usually helps set off vigilante anti-terror agencies.

As of 10 a.m. this morning, the feds were running down leads in three U.S. cities to make sure that these guys are indeed innocent. I’ll update here if there’s any new news.