Frank is fairly close with his description.
I had the chance to examine a similar piece at Coburg in 1985, where his work had been selected for the Second Coburg Glass Prize. I think, but I'm not sure that he may have won one of the prizes, but his work was certainly exciting a lot of interest. I also think I ended up buying a pyramid, which didn't take long to sell. It was a long time ago and it is gradually coming back. I think he had three pieces on show. The Veste Coburg museum had first pick and took the best one, and so I must have had the second best!
It was fairly well accepted at the time, mainly from what he indicated to others (not myself) that he combined engraving techniques with lost wax casting, but what is so special about his casting is that it has the added dimension of being "inside out". This involves not only highly complex mould making but as you pointed out, the mould is broken for each one. But that begs the question - how about the figures on the inside. Well, my recollection was that the plaster models were on the inside, and taking rather a lot of care, he had to remove the plaster from the inside as well. I believe this was done with a flexible drive and diamond engraver, (rather like a dentist's drill), but I'm not a hundred percent sure, as I haven't seen him at work.
Technically these are amazing pieces and extremely difficult to execute. There are loads of things that can go wrong in making work like this!
Of course, if you manage to get the piece out of the mould without any cracks, you then have to grind and polish all the sides of the pyramid.
I always wondered whether any of the editions were completed. I would be surprised if they were.
When searching, it is worth googling Christian Klepsch as well, since some sites have incorrect spelling.
Hope this helps.
I don't know enough about the laser technique, but from the little I do know I think it is unlikely to have been used in these pieces.