Q. How (and why) do the minhagim and halachos relating to the deceased through suicide differ from one who passed away from natural causes?

A. Halacha considers suicide to be tantamount to murder, as the Torah rules (Bereshis 9:5 ), “the blood of your own lives I will demand of you.” (Baba Kama 91b) and looses his part in Olam Habaah, therefore Shulchan Aruch (Y. D. 345: 1) rules that one who commits suicide in principle is denied the after-death honors and privileges of aveilus (mourning): No keria or rending of clothes and eulogies are offered for the deceased, and burial in the main section of the Jewish cemetery is normally not allowed.
There are many details involved in what is considered the honor to the deceased and what is the respect of the living which may be permitted. There are also many specific Halachos that define who in fact committed suicide and who did not, therefore, a competent Rabbi should be consulted.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a