other sources, including articles in "the new york times" and "boston magazine" as well as a press release issued by the united states department of state, have referred to a lack of documentary or testimonial evidence to corroborate the claim that the nsa was involved in his hiring to chas t. main. in addition, the author of the state department release states that the nsa "is a cryptological (codemaking and codebreaking) organization, not an economic organization" and that its missions do not involve "anything remotely resembling placing economists at private companies in order to increase the debt of foreign countries". economic historian niall ferguson writes in his book "the ascent of money" that perkins's contention that the leaders of ecuador (president jaime roldós aguilera) and panama (general omar torrijos) were assassinated by us agents for opposing the interests of the owners of their countries' foreign debt "seems a little odd" in light of the fact that in the 1970s the amount of money that the us had lent to ecuador and panama accounted for less than 0.4% of the total us grants and loans, while in 1990 the exports from the us to those countries accounted for approximately 0.4% of the total us exports (approximately $8 billion). according to ferguson, those "do not seem like figures worth killing for". however, perkins maintains that the motives for such actions, rather than loans, would have been the securing of the panama canal as a permanent united states asset and gaining access to ecuadorian oil. einar greve, the former vice president at chas. t. main who first offered perkins a job there, at first affirmed the overall validity of the book, saying "basically his story is true... what john's book says is, there was a conspiracy to put all these countries on the hook, and that happened. whether or not it was some sinister plot or not is up to interpretation, but many of these countries are still over the barrel and have never been able to repay the loans." however, on being asked by another reporter about the book, greve re-read the book and denied the validity of some of the claims, such as the claim that the nsa had any links to main, or that perkins was seduced by claudine.