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Sieber is one of Europe's most important psychologists – the Georg Sieber Prize, worth *12,500 (£8000) is a testament to his reputation. But he remains a brilliant maverick, a self-employed consultant who advises architects and the police on the best ways to protect buildings and events. His methods are unorthodox, too: like Fitz, the police psychologist in the television series Cracker, he tries to get inside the mind of the terrorist to predict how they will behave.

Today, Sieber has chilling news for the construction industry. "I think there are bombs in buildings right now," he says. Hiding a bomb in a half-finished building is much easier than sneaking one on to a plane – but the results can be just as devastating. A terrorist could plant a radio-activated bomb in a government ministry or company headquarters, then wait years for the right moment to detonate it. Sieber says: "Security on sites should be just as good as security at airports – or even better."

When it comes to airport security, the Israelis are second to none. As you taxi on the runway after landing at Munich airport, one airline stands out from the rest. El-Al, Israel's national carrier, has a tank guarding its plane. A few kilometres south is the Olympic village; five kilometres south of that is a quiet, tree-lined street in the prosperous Nymphenburg district where Sieber has his home and office.

"Society wants to put people my age in an old people's home", says the 69-year-old, who chain-smokes throughout our interview. Defying society, he occupies one-third of an elegant bourgeois villa, in an arrangement that architects call a "live–work space". The walls are lined with religious images, including a watercolour of the Jesuit seminary where Sieber once studied.

Sieber's consultancy, Intelligenz System Transfer, has been in business since 1960, and counts architects, insurance firms and the Catholic church among its clients. Architects come to him for advice on mass evacuation – a hot topic since 11 September. He tells them that when people panic, they all run in the same direction – 45° to the right of the last direction they were facing – for four to five minutes. So, emergency exits should be situated 45° to the right of wherever fleeing people emerge into the ground-floor lobby. Also, people run faster in an anticlockwise direction, so staircases should be designed to allow evacuees to do that.

Sieber says that this, like much of his advice, is ignored by architects, who are more concerned with aesthetics than safety. He claims: "Most architects are not interested in a building's user; they don't know anything about the user." In fact, he has only advised on one construction project that was designed to make the user feel more comfortable – it was a shopping mall, and the owner wanted to put shoppers in a carefree, free-spending mood.

Other terrorists are more patient – a grandfather might plant a bomb for his grandson to explode

In fact, he doubts architects will ever take psychology into account in their designs.

Sieber has followed terrorist organisations for decades. In 1973, he visited Scotland Yard to advise on ill-fated peace negotiations with the IRA. But his ability to get inside their heads is not just the result of experience – it comes from looking at terrorists with clinical detachment. He says: "A terrorist is any person or government that tries to frighten people into acting against their own interests." He treats them the same way as he treats subjects of his research: he tries to explain their behaviour in the past, and predict their behaviour in the future.

His warning of bombs hidden in the fabric of buildings is based on previous attacks. In 1986, Germany's Red Army Faction assassinated Karl Heinz Beckurts, a director of Siemens. Posing as maintenance workers, they dug up the road between his home and office and buried a bomb. An operative hiding in woods nearby waited until Beckurts' car came, then detonated the bomb, killing Beckurts and his driver. Sieber reckons the group borrowed this technique from the IRA.

He says the Beckurts assassination is unlikely to be the last time a terrorist group uses the cover of construction work to hide a bomb. He says: "When you hit a sheet of glass with a hammer, you see an immediate effect. Some terrorists like their attacks to be like that. Others are more patient – a grandfather might plant a bomb for his grandson to explode."

Sieber describes how easily a terrorist could target a building: "On a large construction site, you can have 500 people working at one time. There could be a small subcontractor getting paid off the books. He gets on well with everyone on site, he acts nice, but when everyone else is taking a break, he only needs 10 minutes to put a bomb in a cement wall." And a bomb left in the right place could bring down the entire building. Just as the 11 September hijackers went to flying school, there may be terrorists now training as demolition experts.

With this in mind, Sieber finds site managers remarkably blasé about security. He says that a construction site with 500 workers would need 15 security guards at any one time, checking every person and object entering. Round-the-clock security would require even more staff.