It is hoped that someone who is killed by oppression is counted as a martyr
20-1-2014 | IslamWeb
Question:
I disagreed with my friend about using the word "Shaheed" (martyr) for someone who was killed without right. He claims that we should consider that person to be a martyr, because he was killed by betrayal and oppression, in accordance with the Hadeeth: "Whoever is killed defending himself is a martyr." Is this true? To what extent can this Hadeeth be applied in our current times?
Answer:
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, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
The Muslim who is killed based on tyranny is hoped to be among the martyrs of the Hereafter and it is hoped that he will incur the reward of the martyrs, due to his being killed oppressively. ‘Umar 
prayed: “O Allaah! I ask You for martyrdom in Your Path and to die in the land of Your Messenger, sallallaahu ‘alayhi wa sallam.”
Ibn ‘Abd Al-Barr said: “And this Hadeeth indicates that the one killed in tyranny is a martyr, whether in battle or not and whether in the lands of war or otherwise.”
It is established that the Prophet, sallallaahu ‘alayhi wa sallam, testified that ‘Umar and ‘Uthmaan would both achieve martyrdom, and it is known that they were killed through oppression, may Allaah be pleased with both of them. Al-Munaawi 
said:
The one killed through oppression will have his sins forgiven by his being killed, just as it was reported and authenticated by Ibn Hibbaan and others: “Verily, the sword obliterates sins.” Ibn Mas‘ood said: “If murder comes, it removes all else.” [At-Tabaraani; he related something similar from Al-Hasan ibn ‘Ali]. ‘Aa’ishah said: “Murder does not pass by a sin except that it destroys it;” [Al-Bazzaar: Marfoo’] so if it was not for being killed, his sins might not be forgiven.
This ruling is regarding the one killed through oppression in a general sense. As for the specific individual, then it is hoped that he received what Allaah Promised, but it cannot be completely determined that he is a martyr. We are not able to judge that a specific person is going to Paradise or Hell unless the revelation indicated that (i.e., about a specific person mentioned in the Quran or Sunnah).
Allaah Knows best.