2 Samuel 3:30

And Joab and Abishai his brother killed Abner, because he had slain their brother Asahel at Gibeon in the battle.

2 Samuel 2:19-23

And Asahel ran after Abner, and in going he did not turn to the right hand nor to the left from following Abner.

Proverbs 28:17

A man who is pressed down with the blood of a soul shall flee to the pit; do not let them uphold him.

Acts 28:4

And when the foreigners saw the creature hanging from his hand, they said to one another, No doubt this man is a murderer, whom, being saved from the sea, Justice has not allowed to live.

Treasury of Scripture Knowledge

Summary

So Joab and Abishai his brother slew Abner, because he had slain their brother Asahel at Gibeon in the battle.

Because

Bible References

Slew abner

Proverbs 28:17
A man who is pressed down with the blood of a soul shall flee to the pit; do not let them uphold him.
Acts 28:4
And when the foreigners saw the creature hanging from his hand, they said to one another, No doubt this man is a murderer, whom, being saved from the sea, Justice has not allowed to live.

Because

2 Samuel 2:19
And Asahel ran after Abner, and in going he did not turn to the right hand nor to the left from following Abner.