the meiri on this gemorah says that if ein lo damim you are only not allowed to save him if it is a safek nefashot (not sure if alive or dead). Doesn't safek nefashot have the same din as nefashot mamesh by pikuach nefesh?
Josh Hersch, Woodmere. NY, USA
The footnotes (of Rav Yitzchak Ralbag, #102) in the annotated edition of the Me'iri poses your question in the name of Sefer Dina d'Chayei (the commentary of the Mizrachi on the Semag).
D. Zupnik
It would seem that the Me'iri is suggesting that if the tunnel collapses on a thief, we are not certain whether the thief is still intent on his theft. If there is a possibility that the thief is already dead, we do not save him because of a Sfek Sfeika: maybe he is dead, and even if he is alive maybe he still wants to steal. (The Me'iri himself mentions this latter possibility later in the paragraph.) If he is certainly alive, we save him because of Safek Piku'ach Nefesh (as you said).
Although we normally are Mechalel Shabbos even for a Sfek Sfeika of Piku'ach Nefesh, this case is treated more leniently since the second Safek depends on the mindset of the thief, and not on a physical fact.
M. Kornfeld