It was not, perhaps, the most striking of R. Kenneth Mundy's themes. No news account of the case has bothered to mention it. But sometimes in a court of law a detour -- not the main road -- reaches the jurors. This is a story about one such detour, and the reason the mayor's attorney has chosen to take it.

The detour is as simple as this: Why are there gaps and fuzzy moments in the audio and videotapes of the Vista Hotel sting?

Rich with intimations of conspiracy, that question surfaced on three days out of four in which Mundy cross-examined Hazel Diane "Rasheeda" Moore. Mundy never brought it to a conclusion. But if anywhere there is fertile ground in the minds of the 18 jurors and alternates, Mundy has planted the seeds of a subversive idea.

Could it be that Moore and the FBI have something to hide about the "operation," as Moore prefers to call it, that led to the arrest of D.C. Mayor Marion Barry Jan. 18? Could it be that critical points of the tape have deliberately been obscured?

Mundy never said as much -- quite -- but he has started down that road on several occasions. The first came Friday morning, minutes after Mundy made his initial foray into the Vista sting.

"Whose idea was it to turn the TV sound up so high that it interrupted the audio sound on the tapes we listened to in court?" Mundy asked.

"No one did," Moore replied.

"You did notice there was an awful lot of interruption and a lot of background sound from the television that prevented more clear and precise understanding and listening to an audio tape that was being made? You will agree to that, won't you?" Mundy asked. "If I can explain," Moore began, but Mundy never let her.

Was it not a bit odd, he asked -- and here his rising voice conveyed that he knew well what the answer was -- that the sound stage for an undercover recording should be filled with so much background noise? Did not her FBI handlers arrange with her to turn the volume down? Really? Why not?

For Mundy those were hardly idle questions. Because many of the jurors came into the case with doubts about the sting or hostility to Moore -- and expressed those doubts in two weeks of jury selection -- the last four days have been critical for the defense.

"We've got to get enough out of this {Moore's cross-examination} to carry us through the rest of the case," Mundy said in an interview this week.

Resentment against Moore alone may not translate into acquittal for the mayor, and Mundy is not behaving as though he expects it to. He is therefore planting seeds of doubt, as many as a skeptical imagination permits. Adopting the maxim that nothing is so hard to predict as the reasoning of a juror, Mundy is offering a smorgasbord of reasons for jurors inclined to doubt the government.

The case of the fuzzy recordings was perhaps the most creative. Mundy exploited anomalies not only in the audio portions but also in the pictures. Early in his cross-examination he played a brief tape for the jurors of Moore and an FBI agent in the bathroom of her suite at the Vista Hotel.

The tape showed Moore and the agent conferring three times and making hand signals to one another, while Barry waited in the adjoining bedroom. Why, Mundy asked, was there no sound on this tape? What did the hand signals mean?

On the main tape, why did Moore twice move a chair that stood between the hidden camera and Barry, and why did she block part of the field of view when Barry appeared to take two hits from a crack pipe?

Though these questions were all but irrelevant to any evidentiary element of the case, Assistant U.S. Attorney Judith E. Retchin made a point of addressing them when her chance came for further questions of Moore. Was it not the case, for example, that there was no sound on the bathroom tape because the bathroom door was mostly closed?

Retchin's voice and manner were a study of reasoned reassurance, like a mother trying to show her child that the closet has no ghosts in it after all. The jurors gave no signal whether they were convinced.