Murderer concealing source of red stones (5)
I believe the answer is:
cairn
'stones' is the definition.
(I've seen this before)
'murderer concealing source of red' is the wordplay.
'murderer' becomes 'cain' (Cain who killed Abel).
'concealing' means one lot of letters goes inside another.
'source of' indicates taking the first letters.
The initial letter of 'red' is 'r'.
'cain' going around 'r' is 'CAIRN'.
(Other definitions for cairn that I've seen before include "Heap of stones on mountain-top" , "Stone-pile monument" , "Mound of stones erected as marker" , "Agree" , "Small terrier" .)