WASHINGTON (CNN) -- After a press briefing on another matter on Capitol Hill Wednesday, Sen. Barack Obama, D-Illinois, took several questions on a New York Times article publicizing his "speculative" investments in companies associated with some of his political donors.

Obama walked methodically through what happened, when and why. He explained that he set up a "qualified blind trust" in hopes of insulating himself from knowing which stocks were in a pool of aggressive growth stocks he held.

He said he later dropped the "qualified blind trust" after getting a general mailing to all stockholders from one of the companies he held stocks in and it became clear the trust was not truly blind.

He denied ever knowing what stocks were in the pool -- in particular a biotech company which was working on avian flu at the same time Obama was pushing a bill to boost U.S. government spending on the disease.

Earlier Wednesday Obama's campaign issued a press release that defended the Illinois Democrat's two investments, saying he was unaware of the stock purchases and did not make efforts to aide either company.