Melamine used was the CHEAPEST SCRAP FORM POSSIBLE

Often, the animal feed producers say they do not buy pure melamine, which is used to make plastics and fertilizer, but impure melamine scrap from chemical factories, which is much cheaper than pure melamine.

Feed producers say they believed it to be legal and nontoxic, though they acknowledge they are cheating buyers. Scientists looking at the pet food deaths, however, say melamine scrap may have impurities and related compounds, like cyanuric acid, which could turn it more toxic.

Chinese chemical makers say they also produce a chemical which is a combination of melamine and cyanuric acid, and that feed producers have often sought to purchase scrap material from this product.

Melamine scrap or cyanuric acid scrap often costs one quarter of the price of pure melamine or cyanuric acid and is much cheaper per protein count than wheat or corn meal.

Cyanuric acid scrap is often even cheaper than melamine scrap, producers here say, which is one reason it may have been mixed in or used as a substitute for melamine in the pet food ingredients.

full article (with a strange publish date of tomorrow (05/09/07) can be found here:
http://www.nytimes.com/2007/05/09/business/worldbusiness/09food.html?pagewanted=2&ref=business