

It depends on what secrets are being kept. Here, I would guess that the accused is asking for information relating to secret service deployments, surveillance, and other information on how he was discovered. That information would be useful to future assassins, but doesn’t serve to mitigate his actions or exonerate him.
Just because the accused asks a question with a classified answer does not mean the accused should go free.
These hearings were specifically for determining whether the information the defendant is requesting is exculpatory, or if the requests are specious.and irrelevant. If the judge had ruled the opposite way, the government would have to decide whether to declassify the information, or drop some or all of the charges.
It is very likely that if they chose to declassify and publish the information, they would be able to prosecute many additional charges. They have to balance the value of charging every crime committed against the cost of revealing operational information.