linked - Investigating the Terror

where they had purchased urea or nitric acid. But we did find
where they did purchase a quantity. We have knowledge of a
quantity of chemicals they had purchased. And I had knowledge
of how much chemical was left in the Space Station Storage [the
defendants' alleged storage facility] unused.
I also used that to base on what potential percentage of yield
was.
We are deeply troubled by Williams' rationale. The first factor used--the
yield at Eglin--is problematic. To use Williams' words, Eglin was a
pseudo-laboratory environment, in which chemists did the mixing. It is
impossible to say whether the typical non-laboratory environment --if
there is one--would be better or worse than Eglin. Assuming it would be
worse because of an absence of chemists, one could only speculate about
how much worse. Further, improvised (i.e., homemade ) explosives are
sometimes produced by chemists; so an assumption that non-chemists
made the explosive would be invalid.
The second factor was also inappropriate. Williams' trial testimony about
a non-laboratory yield was offered as an expert opinion based on his
experience making urea nitrate. He was asked what the yield typically
would be in a non-laboratory setting. By basing that opinion on residues
found at the defendants' storage facility and bomb factory, Williams
really offered an opinion on the yield he thought the defendants would
have had, but masked it in the guise of a general opinion. Moreover, it is
pure speculation to say what the defendants' yield would have been from
the discovery of some urea nitrate crystals evidencing spillage.
The third factor, however, is the most problematic. There is a degree of
ambiguity as to what exactly Williams meant. In essence, he said he
based his testimony about non-laboratory yield in part on the amount of
chemicals missing (amounts purchased minus amounts recovered at the
storage facility). Our interpretation of the passage is this: Williams
apparently assumed the Trade Center bomb was made from the
chemicals missing from defendants' storage facility. He estimated, as he
later testified, that the main charge at the Trade Center weighed 1200
pounds. He then divided 1200 by the weight of the applicable amount of
missing urea and nitric acid to give him an estimate of defendants' yield.
He then considered defendants' yield to help him determine nonlaboratory
yield generally.