Yes, One can repent. Allah Almighty says: ‘Say, ˹O Prophet, that Allah says,˺ “O My servants who have exceeded the limits against their souls! Do not lose hope in Allah’s mercy, for Allah certainly forgives all sins.1 He is indeed the All-Forgiving, Most Merciful.’ Az-Zummar 39: 53. However on Judgment day, the victim can get his revenge from his killer.
نعم له توبة ( قُلْ يَا عِبَادِيَ الَّذِينَ أَسْرَفُوا عَلَىٰ أَنفُسِهِمْ لَا تَقْنَطُوا مِن رَّحْمَةِ اللَّهِ ۚ إِنَّ اللَّهَ يَغْفِرُ الذُّنُوبَ جَمِيعًا ۚ إِنَّهُ هُوَ الْغَفُورُ الرَّحِيمُ ) لكن إذا كان يوم القيامة اقتص الله للقاتل من المقتول.