Assalaamu alaykum. If someone is killed illegaly by an unknown person, will all the sins that He committed be transferred to the killer on judgement day?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah and that Muhammad is His slave and Messenger.

If the wronged person does not get his right from the one who wronged him in this world, whether the wrongdoer is a killer or else, and the killed person did not pardon him, then he (the killed) will get his right from him in the Hereafter according to the injustice of the wrongdoer. Some of the good deeds of the wrongdoer will be taken away from him if he has any, otherwise some of the bad deeds of the wronged person will be taken from him and given to the wrongdoer.

Abu Hurayrah narrated that the Prophet said:

“If someone has wronged a person, then he has to seek his forgiveness from that injustice before the Day (of Judgment) on which there would be no dinaar nor dirham. On that Day, if the unjust person has good deeds, then some of them will be taken from him, and if he has no good deeds, then some of the bad deeds of the person he wronged will be taken from him and transmitted to the wrongdoer.” [Al-Bukhari]

Ibn Hajar said:

“The opponents of the sinful believer will take from his good deeds what is equivalent to the punishment of his sins, and if his good deeds are depleted, then some of the sins of his opponents will be taken from them and added to him, and then he will be tortured if he is not pardoned, and when the punishment of those sins end, he will enter Paradise for eternal stay therein  because of his faith.”

On the other hand, Abu Hurayrah narrated that the Prophet said:

“Do you know who is the bankrupt?" They (the Companions) said, "The bankrupt amongst us is the one who has no money and no possessions." He said, "In my community, the bankrupt is the one who will come on the Day of Resurrection with prayer and fasting and zakah (to his credit), but he will come having insulted this one, slandered that one, consumed the wealth of this one, shed the blood of that one, and beaten that one. So each of them will take from his good deeds, and when his good deeds run out before he gives back the right of the people, then part of their sins will be taken from them and cast onto him, then he will be cast into the Fire." [Muslim]

However, there is no evidence that he will bear all the sins of the killed person.

For more benefit, please refer to fatwa 251593.

Allaah Knows best.