1)
What is "Ish ha'Damim"?
1.
Radak citing Targum Yonasan: A man who is Chayav Misah.
2.
Radak: He suspected David of [commanding the] killing of Ish Boshes and Avner. This is why he said (verse 8) "Hashem should return against you all the blood of Beis Sha'ul that you [killed and] ruled in place of him.
3.
Malbim: He hinted to killing Avner, Ish Boshes and Uriyah.
2)
Why did he call him "Ish ha'Beliya'al"?
1.
Malbim: This hints to the episode of Bas Sheva.
