A 25-year-old question about suspicious trading before the 9/11 attacks is back in the spotlight, unsettling for anyone who trusts the official account.

• In the days before the attacks, there was a surge of bets that the two airlines involved would fall and that defense contractors would rise.
• That pattern suggests someone knew the attacks were coming and wanted to make money from them.
• The FBI traced who placed the trades and concluded they were not al-Qaeda — which leaves the question of who they were.
• The trading is documented in the 9/11 report, which found the trades had innocent explanations.

Outlook: Expect renewed pressure around the anniversary to name the traders and release more of the underlying files.