

A Parasha & Halacha Shiur by Rav Yosef Greenwald
וַיֹּאמֶר אֲלֵהֶם רְאוּבֵן אַל תִּשְׁפְּכוּ דָם הַשְׁלִיכוּ אֹתוֹ אֶל הַבּוֹר הַזֶּה אֲשֶׁר בַּמִּדְבָּר וְיָד אַל תִּשְׁלְחוּ בוֹ לְמַעַן הַצִּיל אֹתוֹ מִיָּדָם לַהֲשִׁיבוֹ אֶל אָבִיו.
And Reuven said to them, “Do not spill blood. Cast him into this pit, which is in the desert, but do not lay a hand on him,” in order to save him from their hand, to return him to his father.
(Bereshit 37:22)
How causation correlates with doing.
Reuven was arguing that the brothers ought not kill Yosef directly. Instead, they should place him in a situation where death would come but he would not fall at their hand. Yehuda argued that they would still be responsible for his demise (see Ramban on Pasuk 26).
Indirect causation, Gerama, is discussed in Bava Kama 55b, where we learn that one who commits a tort in this manner is exempt under the laws of man but liable under the laws of Heaven. The distinction between Gerama and B’Yadayim also holds in Halachic realms as diverse as murder and Shabbat.
It must be understood that Gerama is not treated differently to direct action because the likelihood of result is smaller. The Halachic status of Gerama is the same even where the outcome is guaranteed.
Also to be noted is that being responsible only B’Dine Shamayim doesn’t mean that the perpetrator is basically absolved of guilt but has some abstract spiritual obligation. In fact he is culpable for the result he produced. It’s only that Hashem didn’t give Bet Din the authority to adjudicate such cases.