[Repentance of the highway robber]

The answer – and Allah is the One who grants success – is that if the highway robber repents before he falls into the hands of the state, then it is not permissible for anyone to transgress against him, nor to demand from him anything of what he committed during the time he was cutting off the road, whether his crime was against life (killing) or property.
The proof for that is His saying, exalted is He, at the end of the verse about those who wage war (against Allah and His Messenger) and spread corruption on earth: "Except for those who repent before you gain power over them; so know that Allah is All-Forgiving, Most Merciful." [al-Māʾidah:34] And it is narrated in the Sunnah that the Commander of the Faithful, ʿAlī (Peace be upon him), forbade transgressing against the one who had repented during his time. And the outward sense of the words of al-Hādī (Peace be upon him) is that it is not permissible to transgress against the repentant one.
Moreover, the hidden reason and wisdom in that – and Allah knows best – is that making things easy and light upon the highway robber in his repentance is an encouragement for him to repent and to leave off cutting the road. If his repentance were not accepted except after returning everything he had taken, and so on, that would drive him to persist in corruption and highway robbery. And in that there would be such widespread corruption upon the Muslims in general as is not hidden. So Allah, exalted is He, made it light in his repentance, out of His regard, glorified is He, for the general interest of all the Muslims.
And in al-Bayān it states: If he repents before he is captured, his repentance is valid, accepting it is obligatory, and every right of Allah, exalted is He, and of the children of Adam falls from him – even killing, usurpation, theft, and other things which he may have destroyed while in the state of fighting (as a highway robber).
And likewise, if he repents but does not come back to the Imām, or if there is no Imām, then everything Ê falls from him in what is between him and Allah, exalted is He. And this is also the statement of al-Hādī (Peace be upon him). This is the end of what is in al-Bayān and its marginal notes.

Source: Min Thimār al-ʿIlm wa al-Ḥikmah vol.2