Komentarz do Diwrej ha-jamim I 2:7

And the sons of Carmi: Achar Now why do I call him Achar? Was his name not Achan? (It is explained) that [he was called thus] since he troubled Israel by transgressing the devoted thing, and because of him thirty-six thousand (sic) men fell. This is what I explained that whatever derogatory information he can tell, he tells, (but nevertheless) the kingship emanated from them.