The most common and most likely answer to this crossword clue is the 4 letter word ABEL
I've seen this crossword clue in The Sunday Telegraph
A
B
E
L
More clues leading to the result ABEL
- Reportedly talented biblical character
- First murder victim in Lincoln and first in Leicester
- Victim of murderer clever in hearing
- Tag headless murder victim
- Hittable balls not all put over third man
- Gang leader burying extremely brave murder victim
- Early victim of some Bible-basher turned back
- Former US president minimally identified first victim
- President after James B murdered second son?
- President after James B murdered second son!
Buddy explains!
The straight part
We know that "First person killed" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case first person killed = abel.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.