this thread is so nerdy I LOVE IT
re: biolabs -- i've seen a lot of japanese fanstuffs refer to bio3, in english, as a "disposal facility" for biomechanic experiments. i'm not sure where they get this from, since as far as i can tell, the japanese name for biolabs just translates to "biomechanics lab," but i've seen it in numerous works...and how do you get into bio3? by dropping down from what looks like some sort of waste or supply chute, onto a pile of rubble...
anyway, what i always inferred from the whole thing was that yes, rekenber was taking people from the LH slums to experiment on -- there's a huge class difference in all of schwartzvalt (arunafeltz too, but it seems more severe in schwartzvalt because of their level of technology,) so i'm sure they felt that they could use the impoverished however they wanted and no one would really miss them. the angry "voices" you can trigger in bio2, i thought were just memories/spirits of people who perished in the experiments, but the alternate translation of "i hate living" is very interesting and honestly makes more sense
anyway, most of these people probably weren't giving rekenber the powerful results they wanted, so they began using adventurers of the job classes we all know and love. the first class experiments were powerful, but still sort of tame...but by the time they got to trans, oh shit. i assumed that the superpowered (and possibly insane, after all the experiments and imprisonment) trans classes were uncontrollable for rekenber, either causing some sort of fire or rekenber trying to contain them in 3F and burn it down themselves, either way they didn't seem to want anything getting in or out afterward
also, there are no second-class experiments, except for gemini(?) maybe rekenber got greedy and impatient, and jumped straight from wussy first classes to trans, which then backfired on them? THEY WERE NOT PREPARED.
i dunno about the virus idea myself, BUT one thing that may support it (or just be a geeky reference) is the official name of the lab: regenschirm. german for "umbrella" :)