NOVA video
Holocaust Escape Tunnel
Looks like there have been a few examinations of the site. No excavations. A pile of a couple dozen bodies in a photo taken by the Soviet Extraordinary State Commission in August 1944.
The pits were originally used as fuel storage by the Red Army. But instead of killing Jews inside the pits and filling them, the story seems to be that the Nazis dug pits inside the pits for the corpses, then covered the inside pits but not the fuel storage pits.
2021:
Preserving Holocaust History: Geophysical Investigations at the Ponary (Paneriai) Extermination Site
Link
2020:
Mapping Ponar (Paneriai): a reassessment.
Link
2017:
The Forgotten Holocaust in Lithuania - Geophysical Investigations at the Ponary Extermination Site
Link
I came across a few of these papers while looking around for material for the "real world mass grave data" thread.
Uhh, Keen is way better (and funnier) at this than I am, so I'll leave this to the professionals.