Why does it say "b'Nefesh ha'Ish ha'Zeh"?
Rashi: In the sin of taking his Nefesh (killing him).
Why are they not liable for killing him?
Malbim: He sinned, and via him all of us will die (if we do not throw him off the boat). This is not proper! Normally, if one is liable bi'Ydei Shamayim, people who kill him are liable ? "v'Gam Es ha'Goy Asher Ya'avodu Dan Anochi" (Bereishis 15:14), "veha'Elokim Inah l'Yado" (Shemos 21:13). (Here is different, for we stand to die due to him.)
Why did they say "Ka'asher Chafatza Asisa"?
Malbim: This act is not attributed to us, rather, to You. You raised this storm and wanted to drown him in the sea. We must do so ? if we do not throw him, all of us will drown!
