أَقَتَلْتَهُ وَقَدْ شَهِدَ
“Did you kill him although he had already testified?”
The opening أَ marks a question. قَتَلْتَ is a past-tense verb addressed to “you”; the attached هُ refers to the man. وَقَدْ شَهِدَ draws attention to the testimony already given.
فَهَلَّا شَقَقْتَ عَنْ قَلْبِهِ؟
“Why did you not open his heart?”
هَلَّا is used here in a forceful rhetorical challenge, not a literal instruction to open a person's heart. The point is that the other person's inward state was unknown.