That's going to be the problem. Scientists who do not know how to make spore powders will not believe the evidence UNLESS each and every doubting scientist is personally shown exactly how Ivin made the powders.
Do we really want that? What is the alternative? To just let scientists who do not know how to quickly make spore powders endlessly claim that it can't be done quickly? It appears that each and every one of them will find a reporter to report that they don't believe it can be done. Meanwhile, those who know that it CAN be done - and HOW it was done - remain silent because they don't want to INSTRUCT people on how to make lethal anthrax powders.
Tis a puzzlement.
No one can make anything unless they have access to the correct spores. According to the article, a thousand spore samples from around the world were tested and only samples from the Armriid lab matched those used in the attacks. Of the 300 people who had access, relatively few were skilled enough in microbiology to prepare a highly refined spore prep. That should narrow the list of suspects.