A missing eardrum, curiously, signified the first crimes (7)

'the first crimes' is the definition.
'murders' can be an answer for 'crimes'. I am not sure about the 'the first' bit.

'a missing eardrum curiously signified' is the wordplay.
'missing' suggests deleting specific letters.
'curiously' indicates an anagram.
'signified' becomes 's' (this might be a standard abbreviation I've not previously seen).
'eardrum' with 'a' taken out is 'erdrum'.
'erdrum' with letters rearranged gives 'murder'.
'murder'+'s'='MURDERS'