Let me add a couple of disclaimers here - I know that investigating the oddities of published reports puts me in the company of some real nuts and wackos. I also know that questioning or querying the official reports as they come in tends to aggravate some people, who don't even want to hear it. So be it, on both accounts.

Secondly, I have no idea who set up these bombs and I'm not saying I do. My job is to ask questions not to promulgate answers. If you think I'm pointing the finger at group X or group Y and saying "they did it" then you aren't reading what I'm writing.

Thirdly, I am fully aware the investigation is not over and I do hope that when it is completed a lot of these questions will be answered.

In Parts 2 and 3 I examined the oddity of four men who were fully integrated in British society with a lot to live for giving up their lives for a suicide bombing run. In this part, I will examine the strange and inconsistent story of the explosives used.

One oddity is that three of the men - Siddique Khan, Hasib Hussain and Shehzad Tanweer all traveled to Luton in a Nissan Micra. I just happened to see one parked on the street this morning (they're not common in Romania) and I can tell you it's a tiny vehicle. Click here to see an image of one and try to imagine three grown men plus three full-sized backpacks (described in media reports as "large" and visible on the released images as being quite big) filled with explosives in this car. The car has no trunk (or "boot") so the men had to have traveled with an enormous amount of explosives right there jammed in the back seat.

Lindsey Germaine, living in Aylesbury, drove to Luton alone in a Fiat Brava. Again it's a fairly small car (image here) but it is conceivable that there was space for the backpacks and explosives.

But if Germaine brought all the explosives, that would mean he is more closely tied to whomever manufactured the explosives. Indeed all the reports I've seen connect the explosives to the Fiat that Lindsey drove rather than the Micra with the three other men.

There are reports that some explosive material was found in Germaine's Fiat (destroyed in 9 separate "controlled explosions" by the bomb squad). According to media reports, there was a lot of explosive left in the Fiat as well as detonators. Why load up the car with material and detonators you didn't need?

However the factory or place of manufacture has been tied to Leeds, which is where the other three men resided. In fact, the British police say they have found 22 pounds of the explosive used in London inside a bathtub in an apartment in Leeds rented to Magdy al-Nashar, an Egyptian chemistry student.

So if the explosive material was manufactured in Leeds, how did it get to the Luton train station where the four men met up on July 7, parked their cars (leaving some explosive and detonators behind), loaded up their backpacks and then boarded a train to London's King's Cross station, where they parted ways and 3 of them blew up at the same time while the fourth waited 57 minutes to explode?

Actually the material discovered in Leeds was not the finished product, just the potentially dangerous chemicals used to make the alleged explosive. Clearly there doesn't seem to be any reasonable explanation for why someone would have so much of these chemicals (variously described as "available at any pharmacy"). But how did they get to the Luton train station? In the Nissan with the three men or in the Fiat with Germaine? And if they came via Germaine, that means someone moved the explosive from Leeds to Aylesbury beforehand. Germaine's car was a rental, the same as the other three men, who rented theirs.

Except that while some stories describe finding large amounts of the ingredients used to make explosives in al-Nashar's apartment, other sources list it as just "traces". There's a heck of a difference between "traces" and "22 pounds" of material.

So what kind of explosive was found in al-Nashar's apartment? And what kind of explosive was used in the London bombings? You might be surprised that the police have not officially said what was used. But a whole lot of media sources, especially in Britain, are saying that it was TATP or acetone peroxide.

I'm not a biochemist so I'll rely on the experts but TATP is an explosive made from three easy to get ingredients - acetone, hydrogen peroxide and sulphuric acid. I think everyone recognizes "hydrogen peroxide" as an astringent and common liquid for sale in drug stores/pharmacies. "Acetone" sounds fancy but it is more commonly known in the U.S. as fingernail polish remover. The final ingredient, sulphuric acid, isn't for sale in pharmacies or drug stores but it has a lot of uses in chemistry labs and it isn't a controlled substance. So anyone, like say an Egyptian chemistry student, could get their hands on it fairly easily.

I don't know what "traces" might have been found in al-Nashar's apartment but bomb sniffing dogs usually alert on the acetone, which in this case could mean either harmless traces of fingernail polish remover or else something more sinister. If on the other hand "22 pounds" of these chemicals were found that would be something else altogether, although again al-Nashar may have had several different chemical solutions in his apartment for "ordinary" chemistry experiments or dabbling. Either way, with the story constantly changing, it's hard to say.

The problem with TATP is that it's extremely unstable. It's "easy" to make, so a university chemistry student could definitely make it, but it isn't easy to store. It is nicknamed the "Mother of Satan" because it is both extremely powerful and unstable. In fact, it has injured many professional chemists while attempting to make it and it is particularly sensitive to vibration.

Therefore if the explosives used in London were TATP and they were made in Leeds, that would mean that were transported to Luton by car (by way of Aylesbury?), then from Luton to London by train and then put in backpacks and set off a while later in three underground subway stations (and an hour later on a bus). That's a lot of vibrations along this sensitive explosive's journey.

It's worth noting here that Richard Reid, the "shoe bomber", had just 100 grams (4 ounces) of PETN in his shoes when he was arrested. The London bombers have been described as having 10 pounds or 40 times as much explosive in their backpacks. PETN is a more "stable" version of TATP because it has a chemical additive.

Again I remind you that the police have not officially stated what kind of explosives were used. There are mainstream reports that it was C4:

C4 is manufactured mostly in the United States, and is more deadly and efficient than commercial varieties. It is easy to hide, stable, and is often missed by traditional bomb-sniffing detection systems, the newspaper said.

Forensic scientists told the newspaper the construction of the four devices detonated in London was very technically advanced, and unlike any instructions that can be found on the Internet.

There are other reports that it was military TNT originating from "former Soviet satellite countries". Other media reports cite the head of French anti-terrorism, Christophe Chaboud, saying it was some kind of military explosives, from the "Balkans".

There are also reports that the explosive was something called CX123, manufactured in China. Link goes to an interview in German with the chief of the Mossad, Meir Dagan.

The strangest reports are that Jermaine Lindsay bought £900 worth of perfume days before the bombings as some kind of "accelerant":

The Gaultier fragrances were in metal containers which would have splintered into lethal shrapnel in an explosion. Lindsay bought 10.

Terror expert Dr Andrew Silke, of the University of East London, said: "The active ingredient in any perfume is alcohol which can be used in creating devices.

"The effect would be more incendiary, like napalm, rather than highly explosive. It would create more more fire and therefore more burn injuries."

On July 4 Lindsay visited branches of the Fragrance Shop in his home town of Aylesbury, Bucks, and Milton Keynes and Woolworth's in Aylesbury, spending about £300 in each store.

The following day he returned to the Fragrance Shop in Aylesbury searching for a bottle of Boss In Motion perfume he had been unable to buy at Milton Keynes.

"While there, he got really agitated because he wanted a perfume called Boss In Motion Green which comes in a little hard sphere. He was telling them 'I must have one - where can I get one?' Next day he bought it from us."

"Apparently he went back to the shop in Milton Keynes all flustered saying, 'Have you seen a red bag I had?' They didn't have it and I don't know if he ever found it again. But he was really worried."

£900 is about $1,600 dollars. That is one heck of a lot of perfume and cologne. And buying perfume is about the single most expensive way to obtain alcohol. If someone wanted to create a "napalm effect" to enhance the deadliness of a bomb, there are a lot cheaper sources such as isopropyl alcohol (rubbing), ethanol (available to chemists in its pure form), mouthwash, cough syrup and vanilla extract amongst others. Not to mention ordinary "hard liquor".

As for the Gautier coming in small metal containers which would cause shrapnel injuries if exploded - it's much lot cheaper to buy metal "drinking" flasks or thermoses. Walk into any hardware store for a wide variety of cheaper metal objects which could be filled with alcohol.

Clearly a young man like Lindsey, married with a young child and a pregnant wife, buying $1600 worth of purchases on his credit card is strange. However considering that this is about the most wasteful way to obtain alcohol and shrapnel-causing devices, it could be that these were simply gifts for people he was planning on seeing relatively soon.

The investigation continues... stay tuned for Part 5, where the story really falls off the deep end.

Peace