21.   Police said the explosives were powerful enough to level three city blocks.

22.   Police speculated that the explosives used were small or did not fully detonate.

23.   Screening every piece of checked baggage loaded aboard airliners for explosives would be costly and result in crippling delays at U.S. airports, airlines say.

24.   State and federal laws require that explosives be stored in padlocked metal magazines that are resistant to weather erosion, fire, bullets and theft.

25.   Such explosives would be far more powerful than existing non-nuclear explosives.

26.   The betting by experts is that the explosive was a mixture of ingredients known as ammonium nitrate-fuel oil, or ANFO.

27.   The explosive was gunpowder and shavings of wooden matchheads.

28.   The explosives are old and in some cases prone to detonate from heat or shock.

29.   The explosives were gunpowder in bullets a hunter had packed in his suitcase.

30.   The explosive is hard for airport equipment to detect.