Well, blogging was slower than I expected today, because I admit I got totally distracted by the release of Richard Nixon's grand jury testimony from 1975, and I stopped to read his testimony on the 18 1/2 minute gap, which then sent me back to Fred Emery, and, well, there goes a couple of hours.
I can't say I noticed anything too exciting in it...as the AP summary says, Nixon simply insisted that the gap must have been an accident or a malfunction. If you want background, I wrote a while ago about what the gap is and what might have been on it that we would care about -- the short version is that if, as is likely, the President and Chief of Staff Haldeman discussed the Watergate cover-up on the tape, it would have made sense for one of them to try to destroy that evidence -- but we basically already know Nixon's full involvement of the cover-up, so if that's it then at best it would have only provided details. But it's certainly possible that there was evidence of some other crime that we don't have proof of, or even something we don't know about.
I couldn't find my source today, but my memory is that the current best-theory of the experts is that the tape was deliberately erased. If Nixon was the one who did it, then he perjured himself to the Grand Jury and could have been indicted and convicted (the pardon covered his crimes as president, but wouldn't have covered new perjury).
Anyway, I guess I should say something from the testimony...Nixon makes a point of saying that he had had several conversations with Haldeman after the break-in but before the gap take -- it was the first taped conversation, but he had met with Haldeman away from the tapes in Florida and on the plane back to Washington. He implies that therefore there was nothing special about the June 20 gap conversation and it was unlikely to be particularly incriminating, but that's hardly true: we know that Nixon and Haldeman had another conversation later that day (but not subpoenaed at the time the gap showed up) which was incriminating.
As for speculation...There had already been a collective WH decision not to destroy the tapes, but my guess is that someone came across that one and embarked on selective deletion, only to then realize that was both impractical and stupid -- there was far, far, too much incriminating stuff on the tapes. Who? Nixon himself, maybe; it could have been Haldeman, and it could even have been Al Haig.
There are four other topics covered in the testimony, but I haven't looked at those yet. After all, there's news from 2011 to get to also, I suppose!