Is a poor accidental killer, who has fasted for two consecutive months, obligated to pay blood money (diyya) to the victim's guardians, or whatever amount he can afford, and is the blood money waived if he later acquires the means to pay it, especially given that the victim bore some responsibility for crossing a highway when a pedestrian underpass was available?

Accidental killing necessitates expiation (kaffarah (definition)) and blood money (diyah) along with repentance. If the killer fasts for two consecutive months due to the unavailability of a slave to free, then his obligation for expiation is fulfilled, but the blood money remains. It is due to the family of the deceased and is incumbent upon the 'aqilah (male relatives on the father's side). The blood money is waived if the adult and sane guardians of the blood forgive it. Allah Almighty says: (and blood money to be handed over to his family, unless they remit it as charity). The blood money and expiation become binding on the killer if he committed aggression or negligence. In such a case, the blood money is on his 'aqilah, and the expiation is on him alone. However, if there was no aggression or negligence on his part, and he could not have avoided the accident, then there is nothing upon him.