This week has been just another potentially deadly couple of days at the office for Sgt. Dave Thompson of the Massachusetts State Police. He has spent the last 48 hours running to emergency calls around Boston’s Logan Airport—examining suspicious bags, checking out machines that are claiming to find explosives (but so far are actually false positives) and, at one point, dealing with a man carrying two different kinds of gear calling for special scrutiny: he was using a respirator and wearing "moon boots." "We’ve got a lot going on," said a breathless Thompson.

As head of one of the most active bomb squads in the U.S., Thompson, 45, is the unofficial dean of the nation’s aviation bomb corps. He has also been w orried—and warning—about explosives getting on airplanes for the decade he has been on the job, so he knew this day was coming. Such is his reputation that national security officials chose Thompson to handle the case of would-be shoe bomber Richard Reid on board a transatlantic flight that was diverted to Boston in December 2001.

This week proved Thompson right. "We have known terrorists are still very interested in getting a bomb on board. And the challenge is it can look like anything they want it to look like." Intelligence reports have often warned of plots just like the one revealed this week in London—where terrorists evade airport security measures by carrying hidden bomb components onto flights and assembling the devices on board. There have also been recent incidents—like the case in Russia in 2004 where two women strapped on bombs and then detonated them in flight within minutes of each other on two separate flights, killing 95 people.

Before this week when they were banned—perhaps temporarily—Thompson worried about everything from shaving cream to cameras—-since any of them could easily contain bomb components masquerading as innocent materials. And his office is piled high with odd, threatening bits of his business that people have carried into the airport security area, like a can of sterno and a fake grenade.

In one aspect, Thompson had less to worry about than most airport bomb-squad leaders. Thompson and Logan Airport have taken a series of steps to make the airport one of the most secure in the country.

In 2003, Logan became the first U.S. airport to install the most up-to-date explosive detection systems for checked baggage. Logan is also one of fewer than 20 airports (out of some 400 commercial airports in the U.S.) to maintain a full-time bomb squad and Thompson regularly briefs screening managers on new developments in the terrorist arsenal. Earlier this year, Logan became the test site for a profiling system based on a person’s behavior, not race or ethnicity.

The Boston facility was especially motivated to reform, since two of the four 9/11 hijackings originated there. Also, being so far east, Boston fields more than its share of bomb-related incidents or threats since it is the first major U.S. airport encountered by many flights entering the U.S.

Thompson and his colleagues all know the dangers of their work, especially in an era of a global terrorist network that is constantly improving its deadly products and tactics—like the use of secondary devices aimed at those like Thompson who are disarming the bomb. There is also a touch of gallows’ humor: a bumper sticker in Thompson’s office reads, "There is no situation that cannot be solved by the application of explosives."

One of nine children of a Boston fire fighter, Thompson joined the police force at 21 (he took both the fire fighter and police entrance exams, but the police results came back first). A graduate of the bomb training school at Alabama’s Redstone Arsenal, which trains all civilian bomb officials in the U.S., Thompson came to Logan in 1997.

He and his five officers work in shifts around the clock to investigate suspicious packages, or to figure out why an explosive detection machine thinks it has found a threat in a passenger’s suitcase. The machine has a tendency to go off when it encounters items like peanut butter and maple syrup, which mimic the characteristics of some explosives.

On one afternoon in a secure room at Logan, Thompson responded to something in a suitcase that had tested positive for the high energy explosive RDX. The bag, security screeners showed Thompson, was filled with small dark bottles of liquid as well as testing equipment used in explosive detection devices. As Thompson slowly and methodically examined the bottles, the baggage screeners nearby slowly edged away, their eyes widening as Thompson dug further into the suitcase. They silently and slowly moved back, so as not to disturb or distract Thompson. Thompson’s face showed no emotion, but his audience was clearly worried. Notes fellow bomb technician Tim Murray, "We let other people get worked up, but we’re pretty confident in our abilities. Somebody has to stay calm."

The machine was right, but there was no real threat: the bag’s owner turned out to be a repairman for a company that makes explosive detection machines (he was traveling to test some machines outside of Boston), and there actually was liquid explosive used to test the equipment in two small bottles. Thompson trotted up the stairs to the gate and pulled the man aside to tell him that the bottles had been confiscated and that it was illegal to carry such things onboard.

While most of Thompson’s 20 calls a day turn out to be non-events, the case of shoebomber Richard Reid was a notable exception. It was also a stark reminder to Thompson, who like the rest of Logan’s regulars was still dealing with the grim aftermath of 9/11, that explosives remained a terrorist favorite. When the American Airlines flight carrying Reid, who’d already been stripped of his shoes by vigilant flight attendants and passengers on board, was diverted to Logan so Thompson could help handle it, Thompson and his colleague Eddie Anderson, dressed in 100-lb. protective suits and gently took the sneakers off the plane. They neutralized the bomb with a machine (whose workings are classified) that essentially jolts the explosives and detonator apart— which had been expertly hidden in the bottom of the shoes.

Then they took a moment to carefully examine the device. "I thought at first it was a hoax and Reid was just a bumbler," says Thompson, who speaks quietly with a distinctive Boston accent. In fact, it contained a deadly co mbination of chemicals. The main charge was PETN, a powerful plastic explosive. The detonator was TATP, which was used in the London bombings last July. "But when Eddie and I saw the fuse," he continues, his eyes registering the same shock he felt at the time, "the length of it and how it was placed precisely for maximum effectiveness, and cut with surgical precision, I knew we had something," says Thompson with characteristic understatement.

In a test performed afterward, detonation of a similar bomb on an aircraft blew a 2 foot by 2 foot hole in the fuselage—a potentially catastrophic event aboard a plane in flight. "That device was so ingeniously and intricately made that when we told government officials about it, they considered grounding the U.S. fleet again," says Thompson. In the end, the authorities immediately imposed shoe screening for passengers, which remains in effect.

What concerns Thompson now isn’t shoes but sundries—and is why he fully understands this week’s prohibition in carry ons, which may be temporary but which experts say should be made permanent. Explosives can be hidden in anything from a toy to a bottle of cologne. Virtually anything ordinarily made of plastic could be shaped from powerful plastic explosive.

Thompson, who carefully tracks new tactics of bombers through classified briefings and informal contacts with a worldwide network of bomb technicians, knows his opponents are sophisticated. It’s the build-on-board scenario that Thompson says it the key danger, since a pre-assembled bomb stowed in a checked suitcase is more easily identified by authorities than are bomb components brought onboard separately to be assembled in flight. When Thompson is asked, in an ideal world, what he would allow passengers to carry on board, his answer is certain and serious: "Nothing." After this week, U.S. security agencies may be thinking the same thing.