Apparently it was quite common practice on the 3 holer back then, Checkboard.
They'd pull the CB to prevent slat deployment, then move the flap lever to extend the flaps to about 2° and enjoy the ride. The investigation didn't prove anything untoward but I think they were concerned there were a few porky pies being told when they realised the CVR had allegedly been erased after landing.
it was an old wives tale in the company, and the Captain admitted that he had heard of it (as had everyone else), but never attempted it.
Boeing testified that the slats couldn’t deploy any other way (as they would, protecting their aircraft’s reputation. )
The CVR was found erased, and this was in the days when there was an erase button in the cockpit, specifically put there for pilots to erase the tape after a safe flight, as a sop to concerns that management would spy on flight decks in the early days of CVRs. The Captain admitted that it was his habit to erase the tape after normal flights, as did many others back then, but that he didn’t/ couldn’t remember doing so on this flight.
Those items lead to the Captain being accused, BUT
The “pull to CB to deploy the flaps a bit for better high alt cruise” was a stupid idea to anyone that gave it a moments thought. It meant that Boeing would have completely stuffed up the wing design for it to work.. and of course, when the idea was tested, performance was significantly worse, so anyone stupid enough to try it would know it didn’t work.
The slats were shown to deploy independently on failure of the jack, and that happened on other aircraft, despite Boeing’s assurances. The jack was never found on the accident aircraft.
The “erase” switch on the CVR only worked with weight on wheels and park brake set, and the gear was damaged so much that there was no weight on wheels signal, so the Captain couldn’t have erased the CVR even if he wanted to. The erase function was shown to operate with an electrical short, however, and the aircraft damage was such that many items were shorted.
The poor guy saved the aircraft with an amazing bit of flying after a serious upset, and was vilified for it, based on BS accusations