The most common and most likely answer to this crossword clue is the 7 letter word SNIPERS
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More clues leading to the result SNIPERS
Buddy explains!

The straight part
We know that "Killers" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case killers = snipers.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.
What does SNIPERS mean?
SNIPERS noun- A person using long-range small arms for precise attacks from a concealed position.
- Any attacker using a non-contact weapon against a specific target from a concealed position.
- One who shoots from a concealed position.
- One who criticizes.
- (ice hockey slang) A player who specializes in scoring goals.
- A person or automated process set up by a person who or which attempts to win an online auction by placing a bid only seconds before the auction ends, leaving no time for other bidders to respond