What information about Sheikh has he omitted?
It's not about Sheikh directly, more Thompson's claims about Sheikh.
It's also too long to explain here in full, but the summary is something like this.
In
this essay Thompson, amongst other things, makes the case that:
a) post 9/11, Saeed Sheikh gradually appeared in press reports as the 9/11 financier
b) then the ISI/ Sheikh/ Atta story appeared
c) and after that he was largely forgotten as a number of other people were mentioned instead
This then gets used elsewhere to emphasise the importance of the ISI/ Sheikh/ Atta story (ie they had to cover it up).
But to create this effect, though, Thompson
1) doesn't mention the first press report on the financier, which appeared in the Economist, and
2) points to the same information appearing later in the Guardian, but misleads readers by saying it's "not clear" who they're referring to, and failing to mention details that make it sound like someone other than Saeed Sheikh (ie they said it was a man who worked for bin Laden in Sudan), and
3) fails to clearly point out that there's a much better fit for the financier, a man known as Sheikh Saeed who did work for bin Laden in Sudan. and
4) therefore when that man is mentioned later, portrays this as a change of story when it's nothing of the kind
More:
http://www.911myths.com/index.php/Forgetting_Saeed_Sheikh
Individually these are small things, but that's all it takes. An omission, a shift in time, a detail left out, and that's enough to create a false impression.