THE DECISION TO deny bail to former Los Alamos nuclear scientist Wen Ho Lee is the right one given that the government cannot account for seven data tapes he made that contain vast quantities of sensitive nuclear weapons information. Testimony at his bail hearing suggests that the tapes detail knowledge derived from much of the history of U.S. nuclear testing. Mr. Lee's lawyers say that he destroyed the tapes and is willing to take a polygraph test on that assertion. But Mr. Lee -- no doubt to protect his interests at trial -- is apparently not willing to describe precisely when or under what circumstances the destruction took place. Given the gravity of the material in question and the systematic manner in which Mr. Lee appears to have assembled it, the government cannot take at face value his assertion that the tapes no longer exist.

The news, reported by Post staff writer Walter Pincus, that the government is investigating whether Mr. Lee aided his native Taiwan instead of -- or, perhaps, in addition to -- mainland China is another twist in the long and confusing path this case has taken. The shifting nature of the allegations against Mr. Lee continues to be disturbing. He was, after all, initially fingered as the probable leaker of the W-88 warhead design to China. The government now is looking elsewhere for that alleged disclosure and is prosecuting Mr. Lee -- whom it does not accuse of actually passing nuclear secrets to any foreign country -- for the collection and retention of the codes. Now we learn that the foreign power in whose interests he is alleged to have acted may not even be China.

But however shifting the sands may be, the bail hearing testimony is not to be taken lightly. It is difficult to imagine an innocuous reason for the sort of systematic accumulation of this material that the government alleges took place here. And Mr. Lee appears to have accessed the codes -- albeit to retrieve nonclassified material -- during a visit to a Taiwanese military research center last year. Evidence of such behavior in the recent hearing may begin to answer the question of why the government -- while not alleging that Mr. Lee spied -- nonetheless charges in the indictment that he acted "with the intent to injure the United States and with the intent to secure an advantage to a foreign nation."

Mr. Lee is presumed innocent. But there is clearly a huge amount that the public does not know about this case. The possibility that the tapes still may exist and could be disclosed cannot be dismissed, and as long as that possibility is real, bail seems inappropriate.