What caused the structure to fail so quickly on the World Trade Center?

I live in Greece and i am a young engineer. I don’t know anything about 9/11 and the WTC collapse besides what was published through the internet,radios and tv so i imagine you americans can enlighten me on this matter. My question is this:
The official statement of the US government is that W. Trade Towers 1, 2 and 7 collaped due to structural failure through fire in a “pancake” fashion.
Question 1: How can the passport of the highjacker (which proved later was alive and well) pass through the fire and pulverised concrete one piece since the biggest piece the firefighters found is half a phone panel.
Question 2: The pancake theory suggests that the fire heats up the steal suficiently for the floors to brake loose from the steel main columns and start a chain reaction. As an engineer i would expect that according to this theory the core column (consisting of 47 reenforced massive steel colons) should be standing.How could a plane cut all these core colons?
Question 3: Les Robertson (WTC structural engineer) states that they designed a building able to sustain a hit from a Boeing 707 from any side.Frank Demartini (WTC construction manager) adds that WTC was able to sustain multiple aircraft impacts.Aaron Swirsky (WTC architect) also adds that the building was designed to cope with a very bigger hole than the one inflicted to the building. How can there be structural failure on all three towers?
Question 4: How can 110 flours and the core columns fail alltogether and fall apart in just 10.30 secs? This is the speed of a free fall from that height. Can this be done according to the pancake theory?
Question 5: How can there be pools of molten metal on all three towers after their collapse since the metal to melt needs 500 degrees Fahreneit more than the jet fuel even burns?