Why Was the FBI against a Search Warrant?

It does seem like a screwup that the FBI wouldn't want to issue a search warrant against a suspected terrorist before 9/11.

FBI headquarters, however, rejected Minneapolis FBI field agents'
repeated requests for a national security warrant to search Moussaoui's
belongings after he was arrested on Aug. 16, 2001 . One agent, Harry Samit , was
so convinced that Moussaoui was a terrorist that he sent scores of messages to
FBI headquarters pressing for a search warrant.

It might not have made a difference but what kept them from looking inside the bag of a suspected terrorist? I guess they didn't have ironclad proof that Moussaoui was a terrorist and decided to err on the side of not having a lawsuit or something. It just seems like a routine thing for a search warrant to be issued when you are investigating a suspected terrorist. Whatever the case the FBI does look like crap for not following up on the suspicions of their field agents.