Germany investigating men who took pyramid piece

German prosecutors say they're investigating two self-styled researchers who have admitted chipping off a piece from a pyramid's burial chamber in their attempt to prove a theory the structure was built by people pre-dating the ancient Egyptians.

Chemniz prosecutor Ingrid Burghart said Friday that Dominique Goerlitz and Stefan Erdmann are under investigation on suspicion of theft.

Egyptian authorities on Thursday said six Egyptians were already in custody on charges of being accessories to the German men on their expedition last April.

Egyptian prosecutor Hisham Barakat says the men entered the famed Giza pyramids with permits to visit but not excavate, and left with samples of stone from the ramparts of two tombs and the burial room of King Khufu.

The Germans apologized in December, saying their purpose was purely scientific.