Thank you for the website addresses! I am so glad to hear more and more reputable people coming forward with testimonies.
Regarding your first question, I have heard two possible reasons why US is not disclosing that information. The first one is that since many consider USA as a super power for its armed forces weaponry and involvement throughout the globe, disclosing information of such magnitude will put them to compete directly with whatever is visiting us. The competition between nations will no longer exist, or at least will be of little concern when it is compared to something coming from out of this world.
The other reason I have heard of is that US has a "black budget" and part of that money is used in the study and construction of flying vehicles/devices using reverse engineering of alien origin. Who knows... anything is posible! But I would like to see the truth out.

Regards,
Castagna