I decided to do a study of the words and verses for "killing" and "murdering" in scriptures. I began by doing a search for "kill" and "murder" in BibleGateway.com. A search for "kill" also finds "kills," "killing," "killers, etc.; and similarly for "murder."
The search for "kill" in the NRSV came up with a total of 570 verses: 374 OT, 101 NT, and 95 Apoc.
The search for "murder" in the NRSV came up with a total of 125 verses: 77 OT; 31 NT, and 17 Apoc.
I charted which Hebrew and Greek words they used in nearly all 695 verses. (I wasn't able to find the verses in 2 Esdras.) The comments below come from the NRSV.
Before sharing some findings, I also did a comparison of a few other translations. Since a couple of them do not include the Apocrypha, these are the totals for just the OT & NT.
NRSV CEB ESV NASB
"kill" OT 374 400 301 221
"kill" NT 101 110 92 80
TOTAL 475 510 393 301
"murder" OT 77 50 30 32
"murder" NT 31 36 29 27
TOTAL 108 86 59 59
While not delving deeply into the differences, I suspect that the great discrepancy in occurrences from the low numbers in NASB to the high in CEB/NRSV is that the NASB and ESV tend to be more literal. That is, one of the Hebrew words means "to pierce." In some contexts, the piercing causes death, so the meaning of the word in that context is "to kill," which is how the CEB and to a lesser extent the NRSV will translate it. In other contexts it means "to wound." Another Hebrew word means, "to strike" or "to smite." In some contexts, it refers to causing the death of a person, so it means to kill in those contexts. The CEB will make that clear in the translation. A phrase like "to strike with the sword," could mean wounding the other person. The NASB is willing to leave the ambiguity about the meaning.
Some observations from the 695 verses in the NRSV.
The most common Hebrew roots translated, "kill" are:
הגר
נכה
מות
Two observations about these three roots:
1. All are also translated with "murder" in a few contexts. Thus they can refer to both legal and illegal killing; and intentional and unintentional killing. The Torah makes a distinction between intentional and unintentional killing. There were cities of refuge where someone who accidentally killed another could flee and be safe. Those who intentionally killed another (committed murder,) were to be put to death (מות).
2. All three words are used of God killing humans as divine judgment against sin, e.g., the LORD killing the first born sons (Exodus 13:15); or, the statement in Deuteronomy 32:39: "See now that I, even I, am he; there is no god besides me. I kill and I make alive; I wound and I heal; and no one can deliver from my hand." Presumably, such killing by God is justifiable. What these words describe is not always an illegal act.
A different root is the most common one for "murder". It is the one used in the Ten Commandments:
רצח
A few times this root is also translated "kill".
It is never used of God causing the death of a person. Thus, it seems to me, this is the preferred word for illegal or immoral killing, i.e., the crime of "murder." God would not be guilty of murdering human beings.
In the NT, the related words: φονεύω, "to murder," φόνος, "murder," and φονεύς "murderer," are always used for illegal and intentional killing = "murder," except, perhaps, Hebrews 11:37 where the NRSV, ESV, and NASB don't translate φόνος. The phrase in that verse: ἐν φόνῳ μαχαίρης ἀπέθανον, could be translated, "by murder of a sword they were killed."
