Maybe they wouldn’t need explosives at all if they’ve got the knives and a fake bomb. Given the number of knives & cutters they may have intended to meet up with another conspirator or two and take the plane over by going after the crew - one or two sudden, bloody kills to frighten passengers , or a threat to slice a stewardesses’ throat & this might make passengers freeze up long enough to wave the fake bomb in their faces to get everyone to remain seated for good, instead of rushing the hijackers to beating the snot out of them. Maybe the perps hoped it would give them time to work on the cockpit door.
This is a very mystifying story. I read earlier today that some of these things were actually in their checked luggage, which had been checked through on a different flight. Supposedly the one who had checked the baggage onto that flight then did not board it but took a different flight to a different destination where he met the other man. It was the fact that they match up passengers and their baggage (if you’ve checked a bag, you have to board that flight, and he didn’t) that made them search the luggage.